Multi-layered golf balls having foam center with selective weight distribution

ABSTRACT

Multi-layered golf balls having a core made of a foamed composition, preferably polyurethane foam, are provided. The ball includes a dual-layered core having a foam inner core (center) and surrounding outer core layer. The outer core layer may be made from a non-foamed thermoset material such as polybutadiene rubber. The ball further includes an inner cover, preferably made from an ionomer composition comprising an O/X-type acid copolymer, wherein O is α-olefin, and X is a C 3 -C 8  α,β-ethylenically unsaturated carboxylic acid. The outer cover may be made from a non-foamed thermoset or thermoplastic material such as polyurethane. Preferably, the specific gravity of the inner cover is greater than the specific gravity of the outer core, which is greater than the specific gravity of the inner core. The finished ball has good distance and low-spin properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-assigned, co-pending U.S.patent application Ser. No. 14/101,431 having a filing date of Dec. 10,2013, now allowed, the entire contents of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to multi-layered golf ballshaving a core made of a foamed composition. Particularly, the ballincludes a dual-layered core having a foam inner core (center) andsurrounding outer core layer, preferably made from a thermoset rubber.The ball further includes an inner cover, preferably made from athermoplastic ionomer composition; and an outer polyurethane cover. Thecore and inner cover layers have selective weight distribution such thatthe layers have different densities. The finished ball has good distanceand low-spin properties.

2. Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. The inner core is made of a natural orsynthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including ethylene acid copolymer ionomers,polyamides, polyesters, polyurethanes, and polyureas.

In recent years, three-piece, four-piece, and even five-piece balls havebecome more popular. New manufacturing technologies, lower materialcosts, and desirable ball playing performance properties havecontributed to these multi-piece balls becoming more popular. Many golfballs used today have multi-layered cores comprising an inner core andat least one surrounding outer core layer. For example, the inner coremay be made of a relatively soft and resilient material, while the outercore may be made of a harder and more rigid material. The “dual-core”sub-assembly is encapsulated by a cover of at least one layer to providea final ball assembly. Different materials can be used to manufacturethe core and cover and impart desirable properties to the final ball.

The core sub-assembly located inside of the golf ball acts as an engineor spring for the ball. Thus, the composition and construction of thecore is a key factor in determining the resiliency and reboundingperformance of the ball. In general, the rebounding performance of theball is determined by calculating its initial velocity after beingstruck by the face of the golf club and its outgoing velocity aftermaking impact with a hard surface. More particularly, the “Coefficientof Restitution” or “COR” of a golf ball refers to the ratio of a ball'srebound velocity to its initial incoming velocity when the ball is firedout of an air cannon into a rigid vertical plate. The COR for a golfball is written as a decimal value between zero and one. A golf ball mayhave different COR values at different initial velocities. The UnitedStates Golf Association (USGA) sets limits on the initial velocity ofthe ball so one objective of golf ball manufacturers is to maximize CORunder such conditions. Balls with a higher rebound velocity have ahigher COR value. Such golf balls rebound faster, retain more totalenergy when struck with a club, and have longer flight distance asopposed to balls with low COR values. These properties are particularlyimportant for long distance shots. For example, balls having highresiliency and COR values tend to travel a far distance when struck by adriver club from a tee.

The durability, spin rate, and feel of the ball also are importantproperties. In general, the durability of the ball refers to theimpact-resistance of the ball. Balls having low durability appear wornand damaged even when such balls are used only for brief time periods.In some instances, the cover may be cracked or torn. The spin raterefers to the ball's rate of rotation after it is hit by a club. Ballshaving a relatively high spin rate are advantageous for short distanceshots made with irons and wedges. Professional and highly skilledamateur golfers can place a back spin more easily on such balls. Thishelps a player better control the ball and improves shot accuracy andplacement. By placing the right amount of spin on the ball, the playercan get the ball to stop precisely on the green or place a fade on theball during approach shots. On the other hand, recreational players whocannot intentionally control the spin of the ball when hitting it with aclub are less likely to use high spin balls. For such players, the ballcan spin sideways more easily and drift far-off the course, especiallyif it is hooked or sliced. Meanwhile, the “feel” of the ball generallyrefers to the sensation that a player experiences when striking the ballwith the club and it is a difficult property to quantify. Most playersprefer balls having a soft feel, because the player experience a morenatural and comfortable sensation when their club face makes contactwith these balls. Balls having a softer feel are particularly desirablewhen making short shots around the green, because the player senses moreand can place a better touch on such balls. The feel of the ballprimarily depends upon the hardness and compression of the ball.

Manufacturers of golf balls are constantly looking to differentmaterials and ball constructions for improving the playing performanceand other properties of the ball. For example, golf ball manufacturershave looked at ball constructions, wherein the density or specificgravity among the multiple layers of the golf ball is adjusted tocontrol its spin rate. The total weight of a golf ball preferablyconforms to weight limits set by the United States Golf Association(“USGA”). Although the total weight of the golf ball is controlled, thedistribution of weight within the ball can vary. Redistributing theweight or mass of the golf ball either towards the center of the ball ortowards the outer surface of the ball changes its flight and spinproperties.

For example, the weight can be shifted towards the center of the ball toincrease the spin rate as described in Yamada, U.S. Pat. No. 4,625,964,wherein the golf ball contains a core, an intermediate layer, and acover, and the core has a specific gravity of at least 1.50 and adiameter of less than 32 mm, the intermediate layer having a lowerspecific gravity than the core. Chikaraishi et al., U.S. Pat. No.5,048,838 discloses another three-piece golf ball containing a two-piecesolid core and a cover. The dense inner core has a diameter in the rangeof 15-25 mm with a specific gravity of 1.2 to 4.0 and the outer corelayer has a specific gravity of 0.1 to 3.0 less than the specificgravity of the inner core. Gentiluomo, U.S. Pat. No. 5,104,126 disclosesa ball with a dense inner core made of steel, lead, brass, zinc, copper,and a filled elastomer, wherein the core has a specific gravity of atleast 1.25. The inner core is encapsulated by a lower density syntacticfoam composition and this construction is encapsulated by an ionomercover. Yabuki et al., U.S. Pat. No. 5,482,285 discloses a three-piecegolf ball having an inner core and outer core encapsulated by an ionomercover. The specific gravity of the outer core is reduced so that itfalls within the range of 0.2 to 1.0. The specific gravity of the innercore is adjusted so that the total weight of the inner/outer core fallswithin a range of 32.0 to 39.0 g. In other instances, the weight can beshifted to the outside portion of the ball and away from the center. Forexample, Sullivan and Nesbitt, U.S. Pat. No. 6,120,393 discloses golfballs having a low spin rate. The balls comprise a relatively soft,multi-piece core and a hard cover. The inner core is hollow and may befilled with gases, while the outer core layer is made of a soft,resilient material. Sullivan and Nesbitt, U.S. Pat. No. 6,142,887disclose a golf ball containing a core, a thin spherical layer, and apolymeric outer cover. The thin spherical layer comprises a metal,ceramic, or composite material such a silicon carbide, glass, carbon,boron carbide, and aramid materials.

Golf ball manufacturers also have looked at lighter-weight materials,such as foams, for making the inner core. For example, Puckett andCadorniga, U.S. Pat. Nos. 4,836,552 and 4,839,116 disclose one-piece,short distance golf balls made of a foam composition comprising athermoplastic polymer (ethylene acid copolymer ionomer such as Surlyn®)and filler material (microscopic glass bubbles). The density of thecomposition increases from the center to the surface of the ball. Thus,the ball has relatively dense outer skin and a cellular inner core.According to the '552 and '116 patents, by providing a short distancegolf ball, which will play approximately 50% of the distance of aconventional golf ball, the land requirements for a golf course can bereduced 67% to 50%.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece golf ball(FIG. 2) containing a high density center (3) made of steel, surroundedby an outer core (4) of low density resilient syntactic foamcomposition, and encapsulated by an ethylene acid copolymer ionomer(Surlyn®) cover (5). The '126 patent defines the syntactic foam as beinga low density composition consisting of granulated cork or hollowspheres of either phenolic, epoxy, ceramic or glass, dispersed within aresilient elastomer.

Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ballcontaining a core, wherein the core comprising an inner and outerportion, and a cover made of a material such as balata rubber orethylene acid copolymer ionomer. The core is made by foaming, injectinga compressible material, gasses, blowing agents, or gas-containingmicrospheres into polybutadiene or other core material. According to the'889 patent, polyurethane compositions may be used. The compressiblematerial, for example, gas-containing compressible cells may bedispersed in a limited part of the core so that the portion containingthe compressible material has a specific gravity of greater than 1.00.

Golf ball manufacturers have considered foam inner cores over the years,but they have experienced drawbacks with using such foam materials. Forexample, one disadvantage with golf balls having a foam core is the balltends to have low resiliency. That is, the velocity of the ball tends tobe low after being hit by a club and the ball generally travels shortdistances. It would be desirable to have a foam core with improvedresiliency that would allow players to generate higher initial ballspeed. With higher ball speeds, players can make longer distance shots.Particularly, it would be desirable to develop multi-layered foam coreconstructions having the proper weight distribution to provide the ballwith good distance properties. The present invention provides new foamcores and balls having improved weigh distribution, resiliency and otheradvantageous properties, features, and benefits.

SUMMARY OF THE INVENTION

The present invention provides a multi-layered golf ball comprising acore having at least two layers; an inner cover layer; and an outercover layer. In one version, the ball includes a core assemblycomprising: i) an inner core layer (center) comprising a foamedpolyurethane composition, wherein the inner core has a diameter in therange of about 0.100 to about 1.100 inches, preferably about 0.200 toabout 0.900 inches, and a specific gravity (SG_(center)), preferablyabout 0.30 to about 0.95 g/cc, and a center hardness(H_(inner core center)), and ii) an outer core layer comprising a firstnon-foamed thermoset or thermoplastic composition, wherein the outercore layer is disposed about the inner core and has a thickness in therange of about 0.100 to about 0.750 inches, preferably about 0.200 toabout 0.800 inches, and a specific gravity (SG_(outer core)), preferablyabout 0.60 to about 1.20 g/cc and an outer surface hardness(H_(outer surface of OC)). The inner cover comprises a first or secondnon-foamed thermoplastic composition and has a specific gravity(SG_(inner cover)). The outer cover comprises a second or thirdnon-foamed thermoset or thermoplastic composition.

In one preferred embodiment, the SG_(inner cover) is about 1.45 g/cc andthe SG_(inner cover) is greater than the SG_(outer core) and theSG_(outer core) is greater than the SG_(center). Meanwhile, the(H_(inner core center)) is preferably in the range of about 10 to about60 Shore C and the (H_(outer surface of OC)) is preferably in the rangeof about 65 to about 96 Shore C to provide a positive hardness gradientacross the core assembly. In another embodiment, theH_(inner core center) is in the range of about 20 to about 80 Shore Aand the H_(outer surface of OC) is in the range of about 25 to about 63Shore D to provide a positive hardness gradient across the coreassembly.

In one version, the inner core comprises a foam polyurethane compositionprepared from a mixture comprising polyisocyanate, polyol, and curingagent compounds, and blowing agent. Aromatic and aliphaticpolyisocyanates may be used. The foamed polyurethane composition may beprepared by using water as a blowing agent. The water is added to themixture in a sufficient amount to cause the mixture to foam.Surfactants, catalysts, mineral fillers, and other additives may beincluded in the mixture.

Thermoset or thermoplastic materials are used to form the outer corelayer in the present invention. Preferably, the thermoset andthermoplastic materials are non-foamed. Thus, in one embodiment, thedual-core includes a foam inner core (center) and a surroundingnon-foamed thermoset core layer that is preferably made frompolybutadiene rubber. In another embodiment, the dual-core includes afoam inner core (center) and a surrounding non-foamed thermoplastic corelayer. For example, partially or highly neutralized olefin acidcopolymers or non-ionomeric polymers may be used.

The inner cover preferably comprises an ionomer composition comprisingan O/X/Y-type copolymer, wherein O is α-olefin, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is an acrylateselected from alkyl acrylates and aryl acrylates, wherein greater than70% of the acid groups are neutralized with a metal ion. The inner coverlayer preferably has a thickness in the range of about 0.250 to about0.750 inches and specific gravity in the range of about 0.60 to about2.90 g/cc. The outer cover preferably comprises a non-foamed thermosetor thermoplastic polyurethane composition.

The core layers may have different hardness gradients. For example, eachcore layer may have a positive, zero, or negative hardness gradient. Ina first embodiment, the inner core has a positive hardness gradient; andthe outer core layer has a positive hardness gradient. In a secondembodiment, the inner core has a positive hardness gradient, and theouter core layer has zero or negative hardness gradient. In yet anotherversion, the inner core has a zero or negative hardness gradient; andthe outer core layer has a positive hardness gradient. In anotheralternative version, both the inner and outer core layers have zero ornegative hardness gradients. In one embodiment, the center hardness ofthe foamed inner core layer (H_(inner core center)) is in the range ofabout 15 to about 80 Shore A and the outer surface hardness of thefoamed inner core layer (H_(inner core surface)) is in the range ofabout 20 to about 95 Shore A. In another embodiment, theH_(inner core center) is in the range of about 15 to about 80 Shore Aand the H in the inner core surface is range of about 10 to about 75Shore A. The outer core layer may have a midpoint hardness(H_(midpoint of OC)) and an outer surface hardness(H_(outer surface of OC)). In one example, the (H_(midpoint of OC)) isin the range of about 40 to about 87 Shore C and the(H_(outer surface of OC)) is in the range of about 72 to about 95 ShoreC.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a spherical inner core made of a foamedcomposition in accordance with the present invention;

FIG. 2 is a perspective view of one embodiment of upper and lower moldcavities used to make the dual-layered cores of the present invention;

FIG. 3 is a cross-sectional view of a four-piece golf ball having adual-layered core and dual-layered cover made in accordance with thepresent invention;

FIG. 4 is a cross-sectional view of a dual-layered core/inner coverlayer golf ball sub-assembly made in accordance with the presentinvention; and

FIG. 5 is a perspective view of a finished golf ball having a dimpledcover made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having four-piece and five-piececonstructions may be made. Representative illustrations of such golfball constructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a four-piece golf ballcontaining a dual-core (inner core [center] and outer core layers); aninner cover layer; and outer cover layer is made. In another version, afive-piece golf ball containing a dual-core; a casing layer; anddual-cover (inner cover and outer cover layers) is made. As used herein,the term, “casing layer” means a layer of the ball disposed between themulti-layered core sub-assembly and multi-layered cover. The casinglayer also may be referred to as a mantle or intermediate layer. Thediameter and thickness of the different layers along with propertiessuch as hardness and compression may vary depending upon theconstruction and desired playing performance properties of the golfball.

Inner Core Composition

In general, foam compositions are made by forming gas bubbles in apolymer mixture using a foaming (blowing) agent. As the bubbles form,the mixture expands and forms a foam composition that can be molded intoan end-use product having either an open or closed cellular structure.Flexible foams generally have an open cell structure, where the cellswalls are incomplete and contain small holes through which liquid andair can permeate. Such flexible foams are used traditionally forautomobile seats, cushioning, mattresses, and the like. Rigid foamsgenerally have a closed cell structure, where the cell walls arecontinuous and complete, and are used for used traditionally forautomobile panels and parts, building insulation and the like. Manyfoams contain both open and closed cells. It also is possible toformulate flexible foams having a closed cell structure and likewise toformulate rigid foams having an open cell structure.

In the present invention, the inner core (center) comprises alightweight foam thermoplastic or thermoset polymer composition. Thefoam may have an open or closed cellular structure or combinationsthereof and the foam structure may range from a relatively rigid foam toa very flexible foam. Referring to FIG. 1, a foamed inner core (4)having a geometric center (6) and outer skin (8) may be prepared inaccordance with this invention.

A wide variety of thermoplastic and thermoset materials may be used informing the foam composition of this invention including, for example,polyurethanes; polyureas; copolymers, blends and hybrids of polyurethaneand polyurea; olefin-based copolymer ionomer resins (for example,Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000, commerciallyavailable from DuPont; Iotek® ionomers, commercially available fromExxonMobil Chemical Company; Amplify® IO ionomers of ethylene acrylicacid copolymers, commercially available from Dow Chemical Company; andClarix® ionomer resins, commercially available from A. Schulman Inc.);polyethylene, including, for example, low density polyethylene, linearlow density polyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, commercially available from ArkemaInc; cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinggood playing performance properties as discussed further below. By theterm, “hybrids of polyurethane and polyurea,” it is meant to includecopolymers and blends thereof.

Basically, polyurethane compositions contain urethane linkages formed bythe reaction of a multi-functional isocyanate containing two or more NCOgroups with a polyol having two or more hydroxyl groups (OH—OH)sometimes in the presence of a catalyst and other additives. Generally,polyurethanes can be produced in a single-step reaction (one-shot) or ina two-step reaction via a prepolymer or quasi-prepolymer. In theone-shot method, all of the components are combined at once, that is,all of the raw ingredients are added to a reaction vessel, and thereaction is allowed to take place. In the prepolymer method, an excessof polyisocyanate is first reacted with some amount of a polyol to formthe prepolymer which contains reactive NCO groups. This prepolymer isthen reacted again with a chain extender or curing agent polyol to formthe final polyurethane. Polyurea compositions, which are distinct fromthe above-described polyurethanes, also can be formed. In general,polyurea compositions contain urea linkages formed by reacting anisocyanate group (—N═C═O) with an amine group (NH or NH₂). Polyureas canbe produced in similar fashion to polyurethanes by either a one shot orprepolymer method. In forming a polyurea polymer, the polyol would besubstituted with a suitable polyamine. Hybrid compositions containingurethane and urea linkages also may be produced. For example, whenpolyurethane prepolymer is reacted with amine-terminated curing agentsduring the chain-extending step, any excess isocyanate groups in theprepolymer will react with the amine groups in the curing agent. Theresulting polyurethane-urea composition contains urethane and urealinkages and may be referred to as a hybrid. In another example, ahybrid composition may be produced when a polyurea prepolymer is reactedwith a hydroxyl-terminated curing agent. A wide variety of isocyanates,polyols, polyamines, and curing agents can be used to form thepolyurethane and polyurea compositions as discussed further below.

To prepare the foamed polyurethane, polyurea, or other polymercomposition, a foaming agent is introduced into the polymer formulation.In general, there are two types of foaming agents: physical foamingagents and chemical foaming agents.

Physical Foaming Agents.

These foaming agents typically are gasses that are introduced under highpressure directly into the polymer composition. Chlorofluorocarbons(CFCs) and partially halogenated chlorofluorocarbons are effective, butthese compounds are banned in many countries because of theirenvironmental side effects. Alternatively, aliphatic and cyclichydrocarbon gasses such as isobutene and pentane may be used. Inertgasses, such as carbon dioxide and nitrogen, also are suitable. Withphysical foaming agents, the isocyanate and polyol compounds react toform polyurethane linkages and the reaction generates heat. Foam cellsare generated and as the foaming agent vaporizes, the gas becomestrapped in the cells of the foam.

Chemical Foaming Agents.

These foaming agents typically are in the form of powder, pellets, orliquids and they are added to the composition, where they decompose orreact during heating and generate gaseous by-products (for example,nitrogen or carbon dioxide). The gas is dispersed and trapped throughoutthe composition and foams it. For example, water may be used as thefoaming agent. Air bubbles are introduced into the mixture of theisocyanate and polyol compounds and water by high-speed mixingequipment. As discussed in more detail further below, the isocyanatesreact with the water to generate carbon dioxide which fills and expandsthe cells created during the mixing process.

Preferably, a chemical foaming agent is used to prepare the foamcompositions of this invention. Chemical blowing agents may beinorganic, such as ammonium carbonate and carbonates of alkalai metals,or may be organic, such as azo and diazo compounds, such asnitrogen-based azo compounds. Suitable azo compounds include, but arenot limited to, 2,2′-azobis(2-cyanobutane),2,2′-azobis(methylbutyronitrile), azodicarbonamide, p,p′-oxybis(benzenesulfonyl hydrazide), p-toluene sulfonyl semicarbazide, p-toluenesulfonyl hydrazide. Other foaming agents include any of the Celogens®sold by Crompton Chemical Corporation, and nitroso compounds,sulfonylhydrazides, azides of organic acids and their analogs,triazines, tri- and tetrazole derivatives, sulfonyl semicarbazides, ureaderivatives, guanidine derivatives, and esters such as alkoxyboroxines.Also, foaming agents that liberate gasses as a result of chemicalinteraction between components such as mixtures of acids and metals,mixtures of organic acids and inorganic carbonates, mixtures of nitrilesand ammonium salts, and the hydrolytic decomposition of urea may beused. Water is a preferred foaming agent. When added to the polyurethaneformulation, water will react with the isocyanate groups and formcarbamic acid intermediates. The carbamic acids readily decarboxylate toform an amine and carbon dioxide. The newly formed amine can thenfurther react with other isocyanate groups to form urea linkages and thecarbon dioxide forms the bubbles to produce the foam.

During the decomposition reaction of certain chemical foaming agents,more heat and energy is released than is needed for the reaction. Oncethe decomposition has started, it continues for a relatively long timeperiod. If these foaming agents are used, longer cooling periods aregenerally required. Hydrazide and azo-based compounds often are used asexothermic foaming agents. On the other hand, endothermic foaming agentsneed energy for decomposition. Thus, the release of the gasses quicklystops after the supply of heat to the composition has been terminated.If the composition is produced using these foaming agents, shortercooling periods are needed. Bicarbonate and citric acid-based foamingagents can be used as exothermic foaming agents.

Other suitable foaming agents include expandable gas-containingmicrospheres. Exemplary microspheres consist of an acrylonitrile polymershell encapsulating a volatile gas, such as isopentane gas. This gas iscontained within the sphere as a blowing agent. In their unexpandedstate, the diameter of these hollow spheres range from 10 to 17 μm andhave a true density of 1000 to 1300 kg/m³. When heated, the gas insidethe shell increases its pressure and the thermoplastic shell softens,resulting in a dramatic increase of the volume of the microspheres.Fully expanded, the volume of the microspheres will increase more than40 times (typical diameter values would be an increase from 10 to 40μm), resulting in a true density below 30 kg/m³ (0.25 lbs/gallon).Typical expansion temperatures range from 80-190° C. (176-374° F.). Suchexpandable microspheres are commercially available as Expancel® fromExpancel of Sweden or Akzo Nobel.

As an alternative to chemical and physical foaming agents or in additionto such foaming agents, as described above, other types of fillers thatlower the specific gravity of the composition can be used in accordancewith this invention. For example, polymeric, ceramic, and glass unfilledmicrospheres having a density of 0.1 to 1.0 g/cc and an average particlesize of 10 to 250 microns can be used to help lower specific gravity ofthe composition and achieve the desired density and physical properties.

Additionally, BASF polyurethane materials sold under the trade nameCellasto® and Elastocell®, microcellular polyurethanes, Elastopor® Hthat is a closed-cell polyurethane rigid foam, Elastoflex® W flexiblefoam systems, Elastoflex®E semiflexible foam systems, Elastofoam®flexible integrally-skinning systems, Elastolit®D/K/R integral rigidfoams, Elastopan®S, Elastollan® thermoplastic polyurethane elastomers(TPUs), and the like may be used in accordance with the presentinvention. Furthermore, BASF closed-cell, pre-expanded thermoplastic(TPU) polyurethane foam, available under the mark, Infinergy™ also maybe used to form the foam centers of the golf balls in accordance withthis invention. It also is believed these foam materials would be usefulin forming non-center foamed layers in a variety of golf ballconstructions. Such closed-cell, pre-expanded TPU foams are described inPrissok et al., US Patent Applications 2012/0329892; 2012/0297513; and2013/0227861; and U.S. Pat. No. 8,282,851 the disclosures of which arehereby incorporated by reference. Bayer also produces a variety ofmaterials sold as Texin® TPUs, Baytec® and Vulkollan® elastomers,Baymer® rigid foams, Baydur® integral skinning foams, Bayfit® flexiblefoams available as castable, RIM grades, sprayable, and the like thatmay be used. Additional foam materials that may be used herein includepolyisocyanurate foams and a variety of “thermoplastic” foams, which maybe cross-linked to varying extents using free-radical (for example,peroxide) or radiation cross-linking (for example, UV, IR, Gamma, EBirradiation). Also, foams may be prepared from polybutadiene,polystyrene, polyolefin (including metallocene and other single sitecatalyzed polymers), ethylene vinyl acetate (EVA), acrylate copolymers,such as EMA, EBA, Nucrel®-type acid co and terpolymers, ethylenepropylene rubber (such as EPR, EPDM, and any ethylene copolymers),styrene-butadiene, and SEBS (any Kraton-type), PVC, PVDC, CPE(chlorinated polyethylene). Epoxy foams, urea-formaldehyde foams, latexfoams and sponge, silicone foams, fluoropolymer foams and syntacticfoams (hollow sphere filled) also may be used. In particular, siliconefoams may be used. For example, the inner core (center) may be made of asilicone foam rubber and the surrounding outer core layer may be made ofa non-foamed thermoset or thermoplastic composition. The silicone foamrubber composition has good thermal stability. Thus, the thermoset orthermoplastic composition may be molded more effectively over the innercore, and the chemical and physical properties of the inner core willnot degrade substantially

In addition to the polymer and foaming agent, the foam composition alsomay include other ingredients such as, for example, fillers,cross-linking agents, chain extenders, surfactants, dyes and pigments,coloring agents, fluorescent agents, adsorbents, stabilizers, softeningagents, impact modifiers, antioxidants, antiozonants, and the like. Theformulations used to prepare the polyurethane foam compositions of thisinvention preferably contain a polyol, polyisocyanate, water, an amineor hydroxyl curing agent, surfactant, and a catalyst as describedfurther below.

Fillers.

The polyurethane foam composition may contain fillers such as, forexample, mineral filler particulate. Suitable mineral fillerparticulates include compounds such as zinc oxide, limestone, silica,mica, barytes, lithopone, zinc sulfide, talc, calcium carbonate,magnesium carbonate, clays, powdered metals and alloys such as bismuth,brass, bronze, cobalt, copper, iron, nickel, tungsten, aluminum, tin,precipitated hydrated silica, fumed silica, mica, calcium metasilicate,barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide,diatomaceous earth, carbonates such as calcium or magnesium or bariumcarbonate, sulfates such as calcium or magnesium or barium sulfate.Adding fillers to the foam composition provides many benefits includinghelping improve the stiffness and strength of the composition. Themineral fillers tend to help decrease the size of the foam cells andincrease cell density. The mineral fillers also tend to help improve thephysical properties of the foam such as hardness, compression set, andtensile strength. However, in the present invention, it is important theconcentration of fillers in the foam composition be not so high as tosubstantially increase the specific gravity (density) of thecomposition. Particularly, the specific gravity of the inner core ismaintained such that is less than the specific gravity of the outer corelayer as discussed further below. The foam composition may contain somefillers; provided however, the specific gravity of the foam composition(inner core) is kept less than the composition of the surrounding outercore layer. In one embodiment, the foam composition is substantiallyfree of fillers. In another embodiment, the foam composition contains nofillers and consists of a mixture of polyisocyanate, polyol, and curingagent, surfactant, catalyst, and water, the water being added insufficient amount to cause the mixture to foam as discussed above.

If filler is added to the foam composition, clay particulate fillers areparticularly suitable. The clay particulate fillers include Garamite®mixed mineral thixotropes and Cloisite® and Nanofil® nanoclays,commercially available from Southern Clay Products, Inc., and Nanomax®and Nanomer® nanoclays, commercially available from Nanocor, Inc may beused. Other nano-scale materials such as nanotubes and nanoflakes alsomay be used. Also, talc particulate (e.g., Luzenac HAR® high aspectratio talcs, commercially available from Luzenac America, Inc.), glass(e.g., glass flake, milled glass, and microglass), and combinationsthereof may be used. Metal oxide fillers have good heat-stability andmay be added including, for example, aluminum oxide, zinc oxide, tinoxide, barium sulfate, zinc sulfate, calcium oxide, calcium carbonate,zinc carbonate, barium carbonate, tungsten, tungsten carbide, and leadsilicate fillers. Other metal fillers such as, for example, particulate;powders; flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the foam composition.

Surfactants.

The foam composition also may contain surfactants to stabilize the foamand help control the foam cell size and structure. In one preferredversion, the foam composition includes silicone surfactant. In general,the silicone surfactant helps regulate the foam cell size and stabilizesthe cell walls to prevent the cells from collapsing. As discussed above,the liquid reactants react to form the foam rapidly. The “liquid” foamdevelops into solid silicone foam in a relatively short period of time.If a silicone surfactant is not added, the gas-liquid interface betweenthe liquid reactants and expanding gas bubbles may not support thestress. As a result, the cell window can crack or rupture and there canbe cell wall drainage. In turn, the foam can collapse on itself. Addinga silicone surfactant helps create a surface tension gradient along thegas-liquid interface and helps reduce cell wall drainage. The siliconesurfactant has a relatively low surface tension and thus can lower thesurface tension of the foam. It is believed the silicone surfactantorients itself the foam cell walls and lowers the surface tension tocreate the surface tension gradient. Blowing efficiency and nucleationare supported by adding the silicone surfactant and thus more bubblesare created in the system. The silicone surfactant also helps create agreater number of smaller sized foam cells and increases the closed cellcontent of the foam due to the surfactant's lower surface tension. Thus,the cell structure in the foam is maintained as the as gas is preventedfrom diffusing out through the cell walls. Along with the decrease incell size, there is a decrease in thermal conductivity. The resultingfoam material also tends to have greater compression strength andmodulus. These improved physical properties may be due to the increasein closed cell content and smaller cell size.

As discussed further below, in one preferred embodiment, the specificgravity (density) of the foam inner core is less than the specificgravity of the outer core. If mineral filler or other additives areincluded in the foam composition, they should not be added in an amountthat would increase the specific gravity (density) of the foam innercore to a level such that it would be greater than the specific gravityof the outer core layer. If the ball's mass is concentrated towards theouter surface (for example, outer core layers), and the outer core layerhas a higher specific gravity than the inner core, the ball has arelatively high Moment of Inertia (MOI). In such balls, most of the massis located away from the ball's axis of rotation and thus more force isneeded to generate spin. These balls have a generally low spin rate asthe ball leaves the club's face after contact between the ball and club.Such core structures (wherein the specific gravity of the outer core isgreater than the specific gravity of the inner core) is preferred in thepresent invention. Thus, in one preferred embodiment, the concentrationof mineral filler particulate in the foam composition is in the range ofabout 0.1 to about 9.0% by weight.

Properties of Polyurethane Foams

The polyurethane foam compositions of this invention have numerouschemical and physical properties making them suitable for coreassemblies in golf balls. For example, there are properties relating tothe reaction of the isocyanate and polyol components and blowing agent,particularly “cream time,” “gel time,” “rise time,” “tack-free time,”and “free-rise density.” In general, cream time refers to the timeperiod from the point of mixing the raw ingredients together to thepoint where the mixture turns cloudy in appearance or changes color andbegins to rise from its initial stable state. Normally, the cream timeof the foam compositions of this invention is within the range of about20 to about 240 seconds. In general, gel time refers to the time periodfrom the point of mixing the raw ingredients together to the point wherethe expanded foam starts polymerizing/gelling. Rise time generallyrefers to the time period from the point of mixing the raw ingredientstogether to the point where the reacted foam has reached its largestvolume or maximum height. The rise time of the foam compositions of thisinvention typically is in the range of about 60 to about 360 seconds.Tack-free time generally refers to the time it takes for the reactedfoam to lose its tackiness, and the foam compositions of this inventionnormally have a tack-free time of about 60 to about 3600 seconds.Free-rise density refers to the density of the resulting foam when it isallowed to rise unrestricted without a cover or top being placed on themold.

The density of the foam is an important property and is defined as theweight per unit volume (typically, g/cm³) and can be measured per ASTMD-1622. The hardness, stiffness, and load-bearing capacity of the foamare independent of the foam's density, although foams having a highdensity typically have high hardness and stiffness. Normally, foamshaving higher densities have higher compression strength. Surprisingly,the foam compositions used to produce the inner core of the golf ballsper this invention have a relatively low density; however, the foams arenot necessarily soft and flexible, rather, they may be relatively firm,rigid, or semi-rigid depending upon the desired golf ball properties.Tensile strength, tear-resistance, and elongation generally refer to thefoam's ability to resist breaking or tearing, and these properties canbe measured per ASTM D-1623. The durability of foams is important,because introducing fillers and other additives into the foamcomposition can increase the tendency of the foam to break or tearapart. In general, the tensile strength of the foam compositions of thisinvention is in the range of about 20 to about 1000 psi (parallel to thefoam rise) and about 50 to about 1000 psi (perpendicular to the foamrise) as measured per ASTM D-1623 at 23° C. and 50% relative humidity(RH). Meanwhile, the flex modulus of the foams of this invention isgenerally in the range of about 5 to about 45 kPa as measured per ASTMD-790, and the foams generally have a compressive modulus of 200 to50,000 psi.

In another test, compression strength is measured on an Instron machineaccording to ASTM D-1621. The foam is cut into blocks and thecompression strength is measured as the force required to compress theblock by 10%. In general, the compressive strength of the foamcompositions of this invention is in the range of about 100 to about1800 psi (parallel and perpendicular to the foam rise) as measured perASTM D-1621 at 23° C. and 50% relative humidity (RH). The test isconducted perpendicular to the rise of the foam or parallel to the riseof the foam. The Percentage (%) of Compression Set also can be used.This is a measure of the permanent deformation of a foam sample after ithas been compressed between two metal plates under controlled time andtemperature condition (standard—22 hours at 70° C. (158° F.)). The foamis compressed to a thickness given as a percentage of its originalthickness that remained “set.” Preferably, the Compression Set of thefoam is less than ten percent (10%), that is, the foam recovers to apoint of 90% or greater of its original thickness.

Methods of Preparing the Foam Composition

The foam compositions of this invention may be prepared using differentmethods. In one preferred embodiment, the method involves preparing acastable composition comprising a reactive mixture of a polyisocyanate,polyol, water, curing agent, surfactant, and catalyst. A motorized mixercan be used to mix the starting ingredients together and form a reactiveliquid mixture. Alternatively, the ingredients can be manually mixedtogether. An exothermic reaction occurs when the ingredients are mixedtogether and this continues as the reactive mixture is dispensed intothe mold cavities (otherwise referred to as half-molds or mold cups).The mold cavities may be referred to as first and second, or upper andlower, mold cavities. The mold cavities preferably are made of metalsuch as, for example, brass or silicon bronze.

Referring to FIG. 2, the mold cavities are generally indicated at (9)and (10). The lower and upper mold cavities (9, 10) are placed in lowerand upper mold frame plates (11, 12). The frame plates (11, 12) containguide pins and complementary alignment holes (not shown in drawing). Theguide pins are inserted into the alignment holes to secure the lowerplate (11) to the upper plate (12). The lower and upper mold cavities(9, 10) are mated together as the frame plates (11, 12) are fastened.When the lower and upper mold cavities (9, 10) are joined together, theydefine an interior spherical cavity that houses the spherical core. Theupper mold contains a vent or hole (14) to allow for the expanding foamto fill the cavities uniformly. A secondary overflow chamber (16), whichis located above the vent (14), can be used to adjust the amount of foamoverflow and thus adjust the density of the core structure being moldedin the cavities. As the lower and upper mold cavities (9, 10) are matedtogether and sufficient heat and pressure is applied, the foamedcomposition cures and solidifies to form a relatively rigid andlightweight spherical core. The resulting cores are cooled and thenremoved from the mold.

Hardness of the Inner Core

As shown in FIG. 1, a foamed inner core (4) having a geometric center(6) and outer skin (8) may be prepared per the molding method discussedabove. The outer skin (8) is generally a non-foamed region that formsthe outer surface of the core structure. The resulting inner corepreferably has a diameter within a range of about 0.100 to about 1.100inches. For example, the inner core may have a diameter within a rangeof about 0.250 to about 1.000 inches. In another example, the inner coremay have a diameter within a range of about 0.300 to about 0.800 inches.More particularly, the inner core preferably has a diameter size with alower limit of about 0.10 or 0.12 or 0.15 or 0.17 or 0.25 or 0.30 or0.35 or 0.38 or 0.45 or 0.50 or 0.52 or 0.55 inches and an upper limitof about 0.60 or 0.63 or 0.65 or 0.70 or 0.74 or 0.80 or 0.86 or 0.90 or0.95 or 1.00 or 1.02 or 1.10 inches. The outer skin (8) of the innercore is relatively thin preferably having a thickness of less than about0.020 inches and more preferably less than 0.010 inches. In onepreferred embodiment, the foamed core has a “positive” hardness gradient(that is, the outer skin of the inner core is harder than its geometriccenter.)

For example, the geometric center hardness of the inner core(H_(inner core center)), as measured in Shore C units, may be about 10Shore C or greater and preferably has a lower limit of about 10 or 13 or16 or 20 or 25 or 30 or 32 or 34 or 36 or 40 Shore C and an upper limitof about 42 or 44 or 48 or 50 or 52 or 56 or 60 or 62 or 65 or 68 or 70or 74 or 78 or 80 or 84 or 90 Shore C. In one preferred version, thegeometric center hardness of the inner core (H_(inner core center)) isabout 40 Shore C.

When a flexible, relatively soft foam is used, the(H_(inner core center)) of the foam may have a Shore A hardness of about10 or greater, and preferably has a lower limit of 15, 18, 20, 25, 28,30, 35, 38, or 40 Shore A hardness and an upper limit of about 45 or 48,or 50, 54, 58, 60, 65, 70, 80, 85, or 90 Shore A hardness. In onepreferred embodiment, the (H_(inner core center)) of the foam is about55 Shore A.

The H_(inner core center), as measured in Shore D units, is about 15Shore D or greater and more preferably within a range having a lowerlimit of about 15 or 18 or 20 or 22 or 25 or 28 or 30 or 32 or 36 or 40or 44 Shore D and an upper limit of about 45 or 48 or 50 or 52 or 55 or58 or 60 or 62 or 64 or 66 or 70 or 72 or 74 or 78 or 80 or 82 or 84 or88 or 90 Shore D.

Meanwhile, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C, is preferably about 20Shore C or greater and may have, for example, a lower limit of about 10or 14 or 17 or 20 or 22 or 24 or 28 or 30 or 32 or 35 or 36 or 40 or 42or 44 or 48 or 50 Shore C and an upper limit of about 52 or 55 or 58 or60 or 62 or 64 or 66 or 70 or 74 or 78 or 80 or 86 or 88 or 90 or 92 or95 Shore C. When a flexible, relatively soft foam is used, the(H_(inner core surface)) of the foam may have a Shore A hardness ofabout 12 or greater, and preferably has a lower limit of 12, 16, 20, 24,26, 28, 30, 34, 40, 42, 46, or 50 Shore A hardness and an upper limit ofabout 52, 55, 58, 60, 62, 66, 70, 74, 78, 80, 84, 88, 90, or 92 Shore Ahardness. In one preferred embodiment, the (H_(inner core surface)) isabout 60 Shore A. The (H_(inner core surface)), as measured in Shore Dunits, preferably has a lower limit of about 25 or 28 or 30 or 32 or 36or 40 or 44 Shore D and an upper limit of about 45 or 48 or 50 or 52 or55 or 58 or 60 or 62 or 64 or 66 or 70 or 74 or 78 or 80 or 82 or 84 or88 or 90 or 94 or 96 Shore D.

Density of the Inner Core

The foamed inner core preferably has a specific gravity of about 0.20 toabout 1.00 g/cc. That is, the density of the inner core (as measured atany point of the inner core structure) is preferably within the range ofabout 0.20 to about 1.00 g/cc. By the term, “specific gravity of theinner core” (“SG_(inner)”), it is generally meant the specific gravityof the inner core as measured at any point of the inner core structure.It should be understood, however, that the specific gravity values, astaken at different particular points of the inner core structure, mayvary. For example, the foamed inner core may have a “positive” densitygradient (that is, the outer surface (skin) of the inner core may have adensity greater than the geometric center of the inner core.) In onepreferred version, the specific gravity of the geometric center of theinner core (SG_(center of inner core)) is less than 0.80 g/cc and morepreferably less than 0.70 g/cc. More particularly, in one version, the(SG_(center of inner core)) is in the range of about 0.10 to about 0.06g/cc. For example, the (SG_(center of inner core)) may be within a rangehaving a lower limit of about 0.10 or 0.15 of 0.20 or 0.24 or 0.30 or0.35 or 0.37 or 0.40 or 0.42 or 0.45 or 0.47 or 0.50 and an upper limitof about 0.60 or 0.65 or 0.70 or 0.74 or 0.78 or 0.80, or 0.82 or 0.84or 0.85 or 0.88 or 0.90 g/cc. Meanwhile, the specific gravity of theouter surface (skin) of the inner core (SG_(skin of inner core)), in onepreferred version, is greater than about 0.90 g/cc and more preferablygreater than 1.00 g/cc. For example, the (SG_(skin of inner core)) mayfall within the range of about 0.90 to about 1.25 g/cc. Moreparticularly, in one version, the (SG_(skin of inner core)) may have aspecific gravity with a lower limit of about 0.90 or 0.92 or 0.95 or0.98 or 1.00 or 1.02 or 1.06 or 1.10 g/cc and an upper limit of about1.12 or 1.15 or 1.18 or 1.20 or 1.24 or 1.30 or 1.32 or 1.35 g/cc. Inother instances, the outer skin may have a specific gravity of less than0.90 g/cc. For example, the specific gravity of the outer skin(SG_(skin of inner core)) may be about 0.75 or 0.80 or 0.82 or 0.85 or0.88 g/cc. In such instances, wherein both the(SG_(center of inner core)) and (SG_(skin of inner core)) are less than0.90 g/cc, it is still preferred that the (SG_(center of inner core)) beless than the (SG_(skin of inner core)).

Polyisocyanates and Polyols for Making the Polyurethane Foams

As discussed above, in one preferred embodiment, a foamed polyurethanecomposition is used to form the inner core. In general, the polyurethanecompositions contain urethane linkages formed by reacting an isocyanategroup (—N═C═O) with a hydroxyl group (OH). The polyurethanes areproduced by the reaction of multi-functional isocyanates containing twoor more isocyanate groups with a polyol having two or more hydroxylgroups. The formulation may also contain a catalyst, surfactant, andother additives.

In particular, the foam inner core of this invention may be preparedfrom a composition comprising an aromatic polyurethane, which ispreferably formed by reacting an aromatic diisocyanate with a polyol.Suitable aromatic diisocyanates that may be used in accordance with thisinvention include, for example, toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and homopolymersand copolymers and blends thereof. The aromatic isocyanates are able toreact with the hydroxyl or amine compounds and form a durable and toughpolymer having a high melting point. The resulting polyurethanegenerally has good mechanical strength and tear-resistance.

Alternatively, the foamed composition of the inner core may be preparedfrom a composition comprising aliphatic polyurethane, which ispreferably formed by reacting an aliphatic diisocyanate with a polyol.Suitable aliphatic diisocyanates that may be used in accordance withthis invention include, for example, isophorone diisocyanate (IPDI),1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDI”), meta-tetramethylxylyene diisocyanate (TMXDI),trans-cyclohexane diisocyanate (CHDI),1,3-bis(isocyanatomethyl)cyclohexane;1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and copolymersand blends thereof. The resulting polyurethane generally has good lightand thermal stability. Preferred polyfunctional isocyanates include4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylene diphenyldiisocyanate (MDI), and polymeric MDI having a functionality in therange of 2.0 to 3.5 and more preferably 2.2 to 2.5.

Any suitable polyol may be used to react with the polyisocyanate inaccordance with this invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

As discussed further below, chain extenders (curing agents) are added tothe mixture to build-up the molecular weight of the polyurethanepolymer. In general, hydroxyl-terminated curing agents, amine-terminatedcuring agents, and mixtures thereof are used.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds. Suitable catalysts include, but are notlimited to, bismuth catalyst; zinc octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, tributylamine, 1,4-diaza(2,2,2)bicyclooctane,tetramethylbutane diamine, bis[2-dimethylaminoethyl]ether,N,N-dimethylaminopropylamine, N,N-dimethylcyclohexylamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine, diethanolamine,dimethtlethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine,N-ethylmorpholine, 3-dimethylamino-N,N-dimethylpropionamide, andN,N′,N″-dimethylaminopropylhexahydrotriazine; organic acids such asoleic acid and acetic acid; delayed catalysts; and mixtures thereof.Zirconium-based catalysts such as, for example, bis(2-dimethylaminoethyl)ether; mixtures of zinc complexes and amine compounds such asKKAT™ XK 614, available from King Industries; and amine catalysts suchas Niax™ A-2 and A-33, available from Momentive Specialty Chemicals,Inc. are particularly preferred. The catalyst is preferably added in anamount sufficient to catalyze the reaction of the components in thereactive mixture. In one embodiment, the catalyst is present in anamount from about 0.001 percent to about 1 percent, and preferably 0.1to 0.5 percent, by weight of the composition.

In one preferred embodiment, as described above, water is used as thefoaming agent—the water reacts with the polyisocyanate compound(s) andforms carbon dioxide gas which induces foaming of the mixture. Thereaction rate of the water and polyisocyanate compounds affects howquickly the foam is formed as measured per reaction profile propertiessuch as cream time, gel time, and rise time of the foam.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl)ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy)cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof. Di, tri, and tetra-functional polycaprolactone diols such as,2-oxepanone polymer initiated with 1,4-butanediol,2-ethyl-2-(hydroxymethyl)-1,3-propanediol, or2,2-bis(hydroxymethyl)-1,3-propanediol such, may be used.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-)toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3′-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”),4,4′-bis(sec-butylamino)-diphenylmethane,N,N′-dialkylamino-diphenylmethane,trimethyleneglycol-di(p-aminobenzoate),polyethyleneglycol-di(p-aminobenzoate),polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines such asethylene diamine, 1,3-propylene diamine, 2-methyl-pentamethylenediamine, hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, imino-bis(propylamine), imido-bis(propylamine),methylimino-bis(propylamine) (i.e.,N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane (i.e.,3,3′-[1,4-butanediylbis-(oxy)bis]-1-propanamine),diethyleneglycol-bis(propylamine) (i.e.,diethyleneglycol-di(aminopropyl)ether),4,7,10-trioxatridecane-1,13-diamine, 1-methyl-2,6-diamino-cyclohexane,1,4-diamino-cyclohexane, poly(oxyethylene-oxypropylene)diamines, 1,3- or1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane,polyoxypropylene diamines,3,3′-diethyl-5,5′-dichloro-4,4′-diamino-dicyclohexylmethane,polytetramethylene ether diamines, 3,3′,5,5‘-tetraethyl-4,4’-diamino-dicyclohexylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaminocyclohexane)),3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane,(ethylene oxide)-capped polyoxypropylene ether diamines,2,2′,3,3′-tetrachloro-4,4′-diamino-dicyclohexylmethane,4,4′-bis(sec-butylamino)-dicyclohexylmethane; triamines such asdiethylene triamine, dipropylene triamine, (propylene oxide)-basedtriamines (i.e., polyoxypropylene triamines),N-(2-aminoethyl)-1,3-propylenediamine (i.e., N₃-amine), glycerin-basedtriamines, (all saturated); tetramines such asN,N′-bis(3-aminopropyl)ethylene diamine (i.e., N₄-amine) (bothsaturated), triethylene tetramine; and other polyamines such astetraethylene pentamine (also saturated). One suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When a hydroxyl-terminated curing agent is used, the resultingpolyurethane composition contains urethane linkages. On the other hand,when an amine-terminated curing agent is used, any excess isocyanategroups will react with the amine groups in the curing agent. Theresulting polyurethane composition contains urethane and urea linkagesand may be referred to as a polyurethane/urea hybrid.

Core Compositions

As discussed above, a two-layered or dual-core is preferably made,wherein the inner core (center) is surrounded by an outer core layer,and the center is made from a foamed composition. In one preferredembodiment, the outer core layer is made from a non-foamed thermosetcomposition and more preferably from a non-foamed thermoset rubbercomposition.

Suitable thermoset rubber materials that may be used to form the outercore layer include, but are not limited to, polybutadiene, polyisoprene,ethylene propylene rubber (“EPR”), ethylene-propylene-diene (“EPDM”)rubber, styrene-butadiene rubber, styrenic block copolymer rubbers (suchas “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene,“I” is isobutylene, and “B” is butadiene), polyalkenamers such as, forexample, polyoctenamer, butyl rubber, halobutyl rubber, polystyreneelastomers, polyethylene elastomers, polyurethane elastomers, polyureaelastomers, metallocene-catalyzed elastomers and plastomers, copolymersof isobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof. Preferably, the outer core layer is formed from a polybutadienerubber composition.

The thermoset rubber composition may be cured using conventional curingprocesses. Suitable curing processes include, for example,peroxide-curing, sulfur-curing, high-energy radiation, and combinationsthereof. Preferably, the rubber composition contains a free-radicalinitiator selected from organic peroxides, high energy radiation sourcescapable of generating free-radicals, and combinations thereof. In onepreferred version, the rubber composition is peroxide-cured. Suitableorganic peroxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions may further include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur, organicdisulfide, or inorganic disulfide compounds may be added to the rubbercomposition. These compounds also may function as “soft and fastagents.” As used herein, “soft and fast agent” means any compound or ablend thereof that is capable of making a core: 1) softer (having alower compression) at a constant “coefficient of restitution” (COR);and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

In addition, the rubber compositions may include antioxidants. Also,processing aids such as high molecular weight organic acids and saltsthereof may be added to the composition. Other ingredients such asaccelerators, dyes and pigments, wetting agents, surfactants,plasticizers, coloring agents, fluorescent agents, stabilizers,softening agents, impact modifiers, antiozonants, as well as otheradditives known in the art may be added to the rubber composition. Therubber composition also may include filler(s) such as materials selectedfrom carbon black, clay and nanoclay particles as discussed above, talc(e.g., Luzenac HAR® high aspect ratio talcs, commercially available fromLuzenac America, Inc.), glass (e.g., glass flake, milled glass, andmicroglass), mica and mica-based pigments (e.g., Iriodin® pearl lusterpigments, commercially available from The Merck Group), and combinationsthereof. Metal fillers such as, for example, particulate; powders;flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the rubber composition toadjust the specific gravity of the composition as needed. As discussedfurther below, in one preferred embodiment, the inner core layer has aspecific gravity (density) less than the outer core layer's specificgravity; and, the inner cover layer has a specific gravity greater thanthe outer core layer's specific gravity. Thus, if filler is added to thepolybutadiene rubber composition (or other thermoset material) used toform the outer core layer, the concentration of fillers is such that thespecific gravity of the outer core remains greater than the specificgravity of the inner core. However, at the same time, the concentrationof fillers should not be excessive so as to substantially increase thespecific gravity of the composition making the outer core layer'sspecific gravity greater than the inner cover layer's specific gravity.In other words, the specific gravity of the outer core is maintainedsuch that is greater than the specific gravity of the inner core layer;while at the same time, it less than the specific gravity of the innercover layer. The polybutadiene rubber composition may contain somefillers; provided however, the specific gravity of the rubbercomposition (outer core) is kept less than the composition of the innercover layer. In one embodiment, the polybutadiene rubber composition issubstantially free of inert fillers. In another embodiment, thepolybutadiene composition contains no inert fillers and consists of amixture of polybutadiene rubber, free-radical initiator, cross-linkingco-agent, and soft and fast agent as discussed above.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; DIENE 55NF, 70AC, and 320 AC, available fromFirestone Polymers of Akron, Ohio; and PBR-Nd Group II and Group III,available from Nizhnekamskneftekhim, Inc. of Nizhnekamsk, TartarstanRepublic.

The polybutadiene rubber is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of polybutadiene rubber is about 40 to about 95 weightpercent. If desirable, lesser amounts of other thermoset materials maybe incorporated into the base rubber. Such materials include the rubbersdiscussed above, for example, cis-polyisoprene, trans-polyisoprene,balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer,butyl rubber, EPR, EPDM, styrene-butadiene, and the like.

As discussed above, in one preferred embodiment, a thermoset rubbercomposition is used to form the outer core. In alternative embodiments,the outer core layer is made from a thermoplastic material, for example,an ionomer composition.

Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. For purposes of the present disclosure, “HNP” refers to anacid copolymer after at least 70% of all acid groups present in thecomposition are neutralized.

Preferred ionomers are salts of O/X- and O/X/Y-type acid copolymers,wherein O is an α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturatedcarboxylic acid, and Y is a softening monomer. O is preferably selectedfrom ethylene and propylene. X is preferably selected from methacrylicacid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably selected from (meth)acrylate and alkyl (meth)acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth)acrylate, isobutyl (meth)acrylate, methyl(meth)acrylate, and ethyl (meth)acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α,β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth)acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth)acrylic acid is most preferred. As used herein,“(meth)acrylic acid” means methacrylic acid and/or acrylic acid.Likewise, “(meth)acrylate” means methacrylate and/or acrylate.

In a particularly preferred version, highly neutralized E/X- andE/X/Y-type acid copolymers, wherein E is ethylene, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer are used. X is preferably selected from methacrylic acid,acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably an acrylate selected from alkyl acrylates and aryl acrylatesand preferably selected from (meth)acrylate and alkyl (meth)acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth)acrylate, isobutyl (meth)acrylate, methyl(meth)acrylate, and ethyl (meth)acrylate. Preferred E/X/Y-typecopolymers are those wherein X is (meth)acrylic acid and/or Y isselected from (meth)acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, methyl (meth)acrylate, and ethyl (meth)acrylate. Morepreferred E/X/Y-type copolymers are ethylene/(meth)acrylic acid/n-butylacrylate, ethylene/(meth)acrylic acid/methyl acrylate, andethylene/(meth)acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α,β-ethylenically unsaturated mono- ordicarboxylic acid in the acid copolymer is typically from 1 wt. % to 35wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5 wt. %to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %, basedon total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are at leastpartially neutralized with a cation source, optionally in the presenceof a high molecular weight organic acid, such as those disclosed inRajagopalan et al., U.S. Pat. No. 6,756,436, the entire disclosure ofwhich is hereby incorporated herein by reference. The acid copolymer canbe reacted with the optional high molecular weight organic acid and thecation source simultaneously, or prior to the addition of the cationsource. Suitable cation sources include, but are not limited to, metalion sources, such as compounds of alkali metals, alkaline earth metals,transition metals, and rare earth elements; ammonium salts and monoaminesalts; and combinations thereof. Preferred cation sources are compoundsof magnesium, sodium, potassium, cesium, calcium, barium, manganese,copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rareearth metals. The amount of cation used in the composition is readilydetermined based on desired level of neutralization. As discussed above,for HNP compositions, the acid groups are neutralized to 70% or greater,preferably 70 to 100%, more preferably 90 to 100%. In one embodiment, anexcess amount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater. In other embodiments,partially-neutralized compositions are prepared, wherein 10% or greater,normally 30% or greater of the acid groups are neutralized. Whenaluminum is used as the cation source, it is preferably used at lowlevels with another cation such as zinc, sodium, or lithium, sincealuminum has a dramatic effect on melt flow reduction and cannot be usedalone at high levels. For example, aluminum is used to neutralize about10% of the acid groups and sodium is added to neutralize an additional90% of the acid groups.

“Ionic plasticizers” such as organic acids or salts of organic acids,particularly fatty acids, may be added to the ionomer resin. Such ionicplasticizers are used to make conventional ionomer composition moreprocessable as described in the above-mentioned U.S. Pat. No. 6,756,436.In the present invention such ionic plasticizers are optional. In onepreferred embodiment, a thermoplastic ionomer composition is made byneutralizing about 70 wt % or more of the acid groups without the use ofany ionic plasticizer. On the other hand, in some instances, it may bedesirable to add a small amount of ionic plasticizer, provided that itdoes not adversely affect the heat-resistance properties of thecomposition. For example, the ionic plasticizer may be added in anamount of about 10 to about 50 weight percent (wt. %) of thecomposition, more preferably 30 to 55 wt. %.

The organic acids may be aliphatic, mono- or multi-functional(saturated, unsaturated, or multi-unsaturated) organic acids. Salts ofthese organic acids may also be employed. Suitable fatty acid saltsinclude, for example, metal stearates, laureates, oleates, palmitates,pelargonates, and the like. For example, fatty acid salts such as zincstearate, calcium stearate, magnesium stearate, barium stearate, and thelike can be used. The salts of fatty acids are generally fatty acidsneutralized with metal ions. The metal cation salts provide the cationscapable of neutralizing (at varying levels) the carboxylic acid groupsof the fatty acids. Examples include the sulfate, carbonate, acetate andhydroxide salts of metals such as barium, lithium, sodium, zinc,bismuth, chromium, cobalt, copper, potassium, strontium, titanium,tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, orcalcium, and blends thereof. It is preferred the organic acids and saltsbe relatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

Other suitable thermoplastic polymers that may be used to form the innercover layer include, but are not limited to, the following polymers(including homopolymers, copolymers, and derivatives thereof.)

(a) polyesters, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof;

(b) polyamides, polyamide-ethers, and polyamide-esters, and thosedisclosed in U.S. Pat. Nos. 6,187,864, 6,001,930, and 5,981,654, theentire disclosures of which are hereby incorporated herein by reference,and blends of two or more thereof;

(c) polyurethanes, polyureas, polyurethane-polyurea hybrids, and blendsof two or more thereof;

(d) fluoropolymers, such as those disclosed in U.S. Pat. Nos. 5,691,066,6,747,110 and 7,009,002, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof;

(e) polystyrenes, such as poly(styrene-co-maleic anhydride),acrylonitrile-butadiene-styrene, poly(styrene sulfonate), polyethylenestyrene, and blends of two or more thereof;

(f) polyvinyl chlorides and grafted polyvinyl chlorides, and blends oftwo or more thereof;

(g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof;

(h) polyethers, such as polyarylene ethers, polyphenylene oxides, blockcopolymers of alkenyl aromatics with vinyl aromatics and polyamicesters,and blends of two or more thereof;

(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and

(j) polycarbonate/polyester copolymers and blends.

It also is recognized that thermoplastic materials can be “converted”into thermoset materials by cross-linking the polymer chains so theyform a network structure, and such cross-linked thermoplastic materialsmay be used to form the inner cover layers in accordance with thisinvention. For example, thermoplastic polyolefins such as linear lowdensity polyethylene (LLDPE), low density polyethylene (LDPE), and highdensity polyethylene (HDPE) may be cross-linked to form bonds betweenthe polymer chains. The cross-linked thermoplastic material typicallyhas improved physical properties and strength over non-cross-linkedthermoplastics, particularly at temperatures above the crystallinemelting point. Preferably a partially or fully-neutralized ionomer, asdescribed above, is covalently cross-linked to render it into athermoset composition (that is, it contains at least some level ofcovalent, irreversable cross-links). Thermoplastic polyurethanes andpolyureas also may be converted into thermoset materials in accordancewith the present invention.

Modifications in the thermoplastic polymeric structure of thermoplasticscan be induced by a number of methods, including exposing thethermoplastic material to high-energy radiation or through a chemicalprocess using peroxide. Radiation sources include, but are not limitedto, gamma-rays, electrons, neutrons, protons, x-rays, helium nuclei, orthe like. Gamma radiation, typically using radioactive cobalt atoms andallows for considerable depth of treatment, if necessary. For corelayers requiring lower depth of penetration, electron-beam acceleratorsor UV and IR light sources can be used. Useful UV and IR irradiationmethods are disclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576, whichare incorporated herein by reference. The thermoplastic core layers maybe irradiated at dosages greater than 0.05 Mrd, preferably ranging from1 Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and mostpreferably from 4 Mrd to 10 Mrd. In one preferred embodiment, the coresare irradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

The cross-linked thermoplastic material may be created by exposing thethermoplastic to: 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference herein, 2) lower energy radiation,such as ultra-violet (UV) or infra-red (IR) radiation; 3) a solutiontreatment, such as an isocyanate or a silane; 4) incorporation ofadditional free radical initiator groups in the thermoplastic prior tomolding; and/or 5) chemical modification, such as esterification orsaponification, to name a few.

Core Structure

As discussed above, the core of the golf ball of this inventionpreferably has a dual-layered structure comprising inner (center) andouter core layers. Referring to FIG. 3, one version of a golf ball thatcan be made in accordance with this invention is generally indicated at(20). The ball (20) contains a dual-layered core having a center (22)and outer core layer (24) surrounded by an inner cover (26). An outercover (28) is disposed about the inner cover (26). In one embodiment,the inner core (22 a) is relatively small in volume and generally has adiameter within a range of about 0.10 to about 1.10 inches. Moreparticularly, the inner core (22 a) preferably has a diameter size witha lower limit of about 0.15 or 0.25 or 0.35 or 0.45 or 0.50 or 0.55inches and an upper limit of about 0.60 or 0.70 or 0.80 or 0.90 inches.In one preferred version, the diameter of the inner core (22 a) is inthe range of about 0.15 to about 0.80 inches, more preferably about 0.30to about 0.75 inches. In a particularly preferred version, the diameterof the inner core (22 a) is about 0.5 inches. Meanwhile, the outer corelayer (22 b) generally has a thickness within a range of about 0.10 toabout 0.85 inches and preferably has a lower limit of 0.10 or 0.15 or0.20 or 0.25 or 0.30 or 0.32 or 0.35 or 0.40 or 0.45 inches and an upperlimit of 0.50 or 0.52 or 0.60 or 0.65 or 0.68 or 0.70 or 0.75 or 0.78 or0.80 or 0.85 inches. In one preferred version, the outer core layer hasa thickness in the range of about 0.40 to about 0.70 inches, morepreferably about 0.50 to about 0.65 inches. In a particularly preferredversion, the thickness of the outer core (22 b) is about 0.51 inches;and the total diameter of the inner core/outer core sub-assembly isabout 1.53 inches.

Specific Gravity (Density) of Core Layers.

The specific gravity (density) of the respective core layers is animportant property, because they affect the Moment of Inertia (MOI) ofthe ball. In one preferred embodiment, the inner core layer has arelatively low specific gravity (“SG_(inner)”). For example, the innercore layer may have a specific gravity within a range having a lowerlimit of about 0.20 or 0.34 or 0.28 or 0.30 or 0.34 or 0.35 or 0.40 or0.42 or 0.44 or 0.50 or 0.53 or 0.57 or 0.60 or 0.62 or 0.65 or 0.70 or0.75 or 0.77 or 0.80 g/cc and an upper limit of about 0.82 or 0.85 or0.88 or 0.90 or 0.95 or 1.00 or 1.10 or 1.15 or 1.18 or 1.25 g/cc. In aparticularly preferred version, the inner core has a specific gravity ofabout 0.50 g/cc. Also, as discussed below, the specific gravity of theinner core may vary at different particular points of the inner corestructure. That is, there may be a specific gravity gradient in theinner core. For example, in one preferred version, the geometric centerof the inner core has a density in the range of about 0.25 to about 0.75g/cc; while the outer skin of the inner core has a density in the rangeof about 0.75 to about 1.35 g/cc. By the term, “specific gravity of theinner core layer” (“SG_(inner)”), it is generally meant the specificgravity of the outer core layer as measured at any point in the outercore layer.

Meanwhile, the outer core layer preferably has a relatively highspecific gravity (SG_(outer)). Thus, the specific gravity of the innercore layer (SG_(inner)) is preferably less than the specific gravity ofthe outer core layer (SG_(outer)). By the term, “specific gravity of theouter core layer” (“SG_(outer)”), it is generally meant the specificgravity of the outer core layer as measured at any point in the outercore layer. The specific gravity values at different particular pointsin the outer core layer may vary. That is, there may be specific gravitygradients in the outer core layer similar to the gradients found in theinner core. For example, the outer core layer may have a specificgravity within a range having a lower limit of about 0.60 or 0.64 or0.66 or 0.70 or 0.72 or 0.75 or 0.78 or 0.80 or 0.82 or 0.85 or 0.88 or0.90 g/cc and an upper limit of about or 0.95 or 1.00 or 1.05 or 1.10 or1.14 or 1.20 or 1.25 or 1.30 or 1.36 or 1.40 or 1.42 or 1.48 or 1.50 or1.60 or 1.66 or 1.70 1.75 or 2.00 g/cc. In a particularly preferredversion, the inner core has a specific gravity of about 1.05 g/cc.

In general, the specific gravities of the respective pieces of an objectaffect the Moment of Inertia (MOI) of the object. The Moment of Inertiaof a ball (or other object) about a given axis generally refers to howdifficult it is to change the ball's angular motion about that axis. Ifthe ball's mass is concentrated towards the center, less force isrequired to change its rotational rate, and the ball has a relativelylow Moment of Inertia. In such balls, the center piece (that is, theinner core) has a higher specific gravity than the outer piece (that is,the outer core layer). In such balls, most of the mass is located closeto the ball's axis of rotation and less force is needed to generatespin. Thus, the ball has a generally high spin rate as the ball leavesthe club's face after making impact. Because of the high spin rate,amateur golfers may have a difficult time controlling the ball andhitting it in a relatively straight line. Such high-spin balls tend tohave a side-spin so that when a golfer hook or slices the ball, it maydrift off-course and land in a neighboring fairway.

Conversely, if the ball's mass is concentrated towards the outersurface, more force is required to change its rotational rate, and theball has a relatively high Moment of Inertia. In such balls, the centerpiece (that is, the inner core) has a lower specific gravity than theouter piece (that is, the outer core layer). That is, in such balls,most of the mass is located away from the ball's axis of rotation andmore force is needed to generate spin. Thus, the ball has a generallylow spin rate as the ball leaves the club's face after making impact.Because of the low spin rate, amateur golfers may have an easier timecontrolling the ball and hitting it in a relatively straight line. Theball tends to travel a greater distance which is particularly importantfor driver shots off the tee.

As described in Sullivan, U.S. Pat. No. 6,494,795 and Ladd et al., U.S.Pat. No. 7,651,415, the formula for the Moment of Inertia for a spherethrough any diameter is given in the CRC Standard Mathematical Tables,24th Edition, 1976 at 20 (hereinafter CRC reference). In the presentinvention, the finished golf balls preferably have a Moment of Inertiain the range of about 55.0 g./cm² to about 95.0 g./cm², preferably about62.0 g./cm² to about 92.0 g./cm² Samples of finished golf balls havingsuch Moment of Inertia values are provided in the Examples below.

The term, “specific gravity” as used herein, has its ordinary andcustomary meaning, that is, the ratio of the density of a substance tothe density of water at 4° C., and the density of water at thistemperature is 1 g/cm³.

The golf balls of this invention preferably have a high Moment ofInertia and are relatively low spin and long distance. The ball tends totravel a long distance and has less side-spin when a club face makesimpact with the ball. The above-described core construction (wherein theinner core is made of a foamed composition and the surrounding outercore is preferably made of a thermoset rubber composition and thespecific gravity of the outer core is greater than the specific gravityof the inner core [SG_(outer core)>SG_(center)]) contributes to a ballhaving relatively low spin and long distance properties. Moreover, asdiscussed further below, the specific gravity of the inner cover ispreferably greater than the specific gravity of the outer core(SG_(inner cover)>SG_(outer core)). Thus, most of the ball's mass islocated away from the ball's center (axis of rotation) and this helpsproduce even lower spin rate and longer distance properties. The foamcores and resulting balls also have relatively high resiliency so theball will reach a relatively high velocity when struck by a golf cluband travel a long distance.

In particular, the inner foam cores of this invention preferably have aCoefficient of Restitution (COR) of about 0.300 or greater; morepreferably about 0.400 or greater, and even more preferably about 0.450or greater. The resulting balls containing the dual-layered coreconstructions of this invention and cover of at least one layerpreferably have a COR of about 0.700 or greater, more preferably about0.730 or greater; and even more preferably about 0.750 to 0.810 orgreater.

The USGA has established a maximum weight of 45.93 g (1.62 ounces) forgolf balls. For play outside of USGA rules, the golf balls can beheavier. In one preferred embodiment, the weight of the multi-layeredcore is in the range of about 28 to about 42 grams. Also, golf ballsmade in accordance with this invention can be of any size, although theUSGA requires that golf balls used in competition have a diameter of atleast 1.68 inches. For play outside of United States Golf Association(USGA) rules, the golf balls can be of a smaller size. Normally, golfballs are manufactured in accordance with USGA requirements and have adiameter in the range of about 1.68 to about 1.80 inches. As discussedfurther below, the golf ball contains a multi-layered cover and also maycontain intermediate (casing) layers, so the thickness levels of theselayers also must be considered. Thus, in general, the dual-layer corestructure normally has an overall diameter within a range having a lowerlimit of about 1.00 or 1.20 or 1.30 or 1.40 inches and an upper limit ofabout 1.58 or 1.60 or 1.62 or 1.66 inches, and more preferably in therange of about 1.3 to 1.65 inches. In one embodiment, the diameter ofthe core sub-assembly is in the range of about 1.45 to about 1.62inches. In turn, the casing layers (optional) and cover layers provide aball having a diameter of at least 1.68 inches to meet USGA regulations.

Hardness of Core Layers.

The hardness of the core sub-assembly (inner core and outer core layer)also is an important property. In general, cores with relatively highhardness values have higher compression and tend to have good durabilityand resiliency. However, some high compression balls are stiff and thismay have a detrimental effect on shot control and placement. Thus, theoptimum balance of hardness in the core sub-assembly needs to beattained.

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center); and the outer core layer has a“positive” hardness gradient (that is, the outer surface of the outercore layer is harder than the inner surface of the outer core layer.) Insuch cases where both the inner core and outer core layer each has a“positive” hardness gradient, the outer surface hardness of the outercore layer is preferably greater than the hardness of the geometriccenter of the inner core. In one preferred version, the positivehardness gradient of the inner core is in the range of about 2 to about40 Shore C units and even more preferably about 10 to about 25 Shore Cunits; while the positive hardness gradient of the outer core is in therange of about 2 to about 20 Shore C and even more preferably about 3 toabout 10 Shore C.

In an alternative version, the inner core may have a positive hardnessgradient; and the outer core layer may have a “zero” hardness gradient(that is, the hardness values of the outer surface of the outer corelayer and the inner surface of the outer core layer are substantiallythe same) or a “negative” hardness gradient (that is, the outer surfaceof the outer core layer is softer than the inner surface of the outercore layer.) For example, in one version, the inner core has a positivehardness gradient; and the outer core layer has a negative hardnessgradient in the range of about 2 to about 25 Shore C. In a secondalternative version, the inner core may have a zero or negative hardnessgradient; and the outer core layer may have a positive hardnessgradient. Still yet, in another embodiment, both the inner core andouter core layers have zero or negative hardness gradients.

In general, hardness gradients are further described in Bulpett et al.,U.S. Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which arehereby incorporated by reference. Methods for measuring the hardness ofthe inner core and outer core layers along with other layers in the golfball and determining the hardness gradients of the various layers aredescribed in further detail below. The core layers have positive,negative, or zero hardness gradients defined by hardness measurementsmade at the outer surface of the inner core (or outer surface of theouter core layer) and radially inward towards the center of the innercore (or inner surface of the outer core layer). These measurements aremade typically at 2-mm increments as described in the test methodsbelow. In general, the hardness gradient is determined by subtractingthe hardness value at the innermost portion of the component beingmeasured (for example, the center of the inner core or inner surface ofthe outer core layer) from the hardness value at the outer surface ofthe component being measured (for example, the outer surface of theinner core or outer surface of the outer core layer).

Positive Hardness Gradient.

For example, if the hardness value of the outer surface of the innercore is greater than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface harder than its geometriccenter), the hardness gradient will be deemed “positive” (a largernumber minus a smaller number equals a positive number.) For example, ifthe outer surface of the inner core has a hardness of 67 Shore C and thegeometric center of the inner core has a hardness of 60 Shore C, thenthe inner core has a positive hardness gradient of 7. Likewise, if theouter surface of the outer core layer has a greater hardness value thanthe inner surface of the outer core layer, the given outer core layerwill be considered to have a positive hardness gradient.

Negative Hardness Gradient.

On the other hand, if the hardness value of the outer surface of theinner core is less than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface softer than its geometriccenter), the hardness gradient will be deemed “negative.” For example,if the outer surface of the inner core has a hardness of 68 Shore C andthe geometric center of the inner core has a hardness of 70 Shore C,then the inner core has a negative hardness gradient of 2. Likewise, ifthe outer surface of the outer core layer has a lesser hardness valuethan the inner surface of the outer core layer, the given outer corelayer will be considered to have a negative hardness gradient.

Zero Hardness Gradient.

In another example, if the hardness value of the outer surface of theinner core is substantially the same as the hardness value of the innercore's geometric center (that is, the surface of the inner core hasabout the same hardness as the geometric center), the hardness gradientwill be deemed “zero.” For example, if the outer surface of the innercore and the geometric center of the inner core each has a hardness of65 Shore C, then the inner core has a zero hardness gradient. Likewise,if the outer surface of the outer core layer has a hardness valueapproximately the same as the inner surface of the outer core layer, theouter core layer will be considered to have a zero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 3 Shore C or greater, preferably 7Shore C or greater, more preferably 10 Shore C, and even more preferably20 Shore C or greater. The term, “zero hardness gradient” as used hereinmeans a hardness gradient of less than 3 Shore C, preferably less than 1Shore C and may have a value of zero or negative 1 to negative 10 ShoreC. The term, “negative hardness gradient” as used herein means ahardness value of less than zero, for example, negative 3, negative 5,negative 7, negative 10, negative 15, or negative 20 or negative 25. Theterms, “zero hardness gradient” and “negative hardness gradient” may beused herein interchangeably to refer to hardness gradients of negative 1to negative 10.

The inner core preferably has a geometric center hardness(H_(inner core center)) of about 5 Shore D or greater. For example, the(H_(inner core center)) may be in the range of about 5 to about 88 ShoreD and more particularly within a range having a lower limit of about 5or 10 or 18 or 20 or 26 or 30 or 34 or 36 or 38 or 42 or 48 or 50 or 52Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62 or 64 or68 or 70 or 74 or 76 or 80 or 82 or 84 or 88 Shore D. In anotherexample, the center hardness of the inner core (H_(inner core center)),as measured in Shore C units, is preferably about 10 Shore C or greater;for example, the H_(inner core center) may have a lower limit of about10 or 14 or 16 or 20 or 23 or 24 or 28 or 31 or 34 or 37 or 40 or 44Shore C and an upper limit of about 46 or 48 or 50 or 51 or 53 or 55 or58 or 61 or 62 or 65 or 68 or 71 or 74 or 76 or 78 or 79 or 80 or 84 or90 Shore C. Concerning the outer surface hardness of the inner core(H_(inner core surface)), this hardness is preferably about 12 Shore Dor greater; for example, the H_(inner core surface) may fall within arange having a lower limit of about 12 or 15 or 18 or 20 or 22 or 26 or30 or 34 or 36 or 38 or 42 or 48 or 50 or 52 Shore D and an upper limitof about 54 or 56 or 58 or 60 or 62 or 70 or 72 or 75 or 78 or 80 or 82or 84 or 86 or 90 Shore D. In one version, the outer surface hardness ofthe inner core (H_(inner core surface)), as measured in Shore C units,has a lower limit of about 13 or 15 or 18 or 20 or 22 or 24 or 27 or 28or 30 or 32 or 34 or 38 or 44 or 47 or 48 Shore C and an upper limit ofabout 50 or 54 or 56 or 61 or 65 or 66 or 68 or 70 or 73 or 76 or 78 or80 or 84 or 86 or 88 or 90 or 92 Shore C. In another version, thegeometric center hardness (H_(inner core center)) is in the range ofabout 10 Shore C to about 50 Shore C; and the outer surface hardness ofthe inner core (H_(inner core surface)) is in the range of about 5 ShoreC to about 50 Shore C.

On the other hand, the outer core layer preferably has an outer surfacehardness (H_(outer surface of OC)) of about 40 Shore D or greater, andmore preferably within a range having a lower limit of about 40 or 42 or44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90Shore D. The outer surface hardness of the outer core layer(H_(outer surface of OC)), as measured in Shore C units, preferably hasa lower limit of about 40 or 42 or 45 or 48 or 50 or 54 or 58 or 60 or63 or 65 or 67 or 720 or 72 or 73 or 76 Shore C, and an upper limit ofabout 78 or 80 or 84 or 87 or 88 or 89 or 90 or 92 or 95 Shore C. And,the inner surface of the outer core layer (H_(inner surface of OC)) ormidpoint hardness of the outer core layer (H_(midpoint of OC)),preferably has a hardness of about 40 Shore D or greater, and morepreferably within a range having a lower limit of about 40 or 42 or 44or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or 60or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90 ShoreD. The inner surface hardness (H_(inner surface of OC)) or midpointhardness (H_(midpoint of OC)) of the outer core layer, as measured inShore C units, preferably has a lower limit of about 40 or 42 or 44 or45 or 47 or 50 or 52 or 54 or 55 or 58 or 60 or 63 or 65 or 67 or 70 or73 or 75 Shore C, and an upper limit of about 78 or 80 or 85 or 88 or 89or 90 or 92 or 95 Shore C.

In one embodiment, the outer surface hardness of the outer core layer(H_(outer surface of OC)), is less than the outer surface hardness(H_(inner core surface)) or midpoint hardness (H_(midpoint of OC)), ofthe inner core by at least 3 Shore C units and more preferably by atleast 5 Shore C.

In a second embodiment, the outer surface hardness of the outer corelayer (H_(outer surface of OC)), is greater than the outer surfacehardness (H_(inner core surface)) or midpoint hardness(H_(midpoint of OC)), of the inner core by at least 3 Shore C units andmore preferably by at least 5 Shore C.

As discussed above, the inner core is preferably formed from a foamedthermoplastic or thermoset composition and more preferably foamedpolyurethanes. And, the outer core layer is formed preferably from anon-foamed thermoset composition such as polybutadiene rubber.

The core structure also has a hardness gradient across the entire coreassembly. In one embodiment, the (H_(inner core center)) is in the rangeof about 10 to about 60 Shore C, preferably about 13 to about 55 Shore Cand more preferably about 15 to about 50 Shore C; and the(H_(outer surface of OC)) is in the range of about 65 to about 96 ShoreC, preferably about 68 to about 94 Shore C and more preferably about 75to about 92 Shore C, to provide a positive hardness gradient across thecore assembly.

In another embodiment, the H_(inner core center) is in the range ofabout 20 to about 70 Shore A and the H_(outer surface of OC) is in therange of about 25 to about 58 Shore D to provide a positive hardnessgradient across the core assembly. The gradient will vary based onseveral factors including, but not limited to, the dimensions of theinner core and outer core layers.

The inner core preferably has a diameter in the range of about 0.100 toabout 1.100 inches. For example, the inner core may have a diameterwithin a range of about 0.100 to about 0.500 inches. In another example,the inner core may have a diameter within a range of about 0.300 toabout 0.800 inches. More particularly, the inner core may have adiameter size with a lower limit of about 0.10 or 0.12 or 0.15 or 0.25or 0.30 or 0.35 or 0.45 or 0.55 inches and an upper limit of about 0.60or 0.65 or 0.70 or 0.80 or 0.90 or 1.00 or 1.10 inches. As far as theouter core layer is concerned, it preferably has a thickness in therange of about 0.100 to about 0.750 inches. For example, the lower limitof thickness may be about 0.050 or 0.100 or 0.150 or 0.200 or 0.250 or0.300 or 0.340 or 0.400 and the upper limit may be about 0.500 or 0.550or 0.600 or 0.650 or 0.700 or 0.750 inches.

Dual-layered core structures containing layers with various thicknessand volume levels may be made in accordance with this invention. Forexample, in one version, the total diameter of the core structure is0.20 inches and the total volume of the core structure is 0.23 cc. Moreparticularly, in this example, the diameter of the inner core is 0.10inches and the volume of the inner core is 0.10 cc; while the thicknessof the outer core is 0.100 inches and the volume of the outer core is0.13 cc. In another version, the total core diameter is about 1.55inches and the total core volume is 31.96 cc. In this version, the outercore layer has a thickness of 0.400 inches and volume of 28.34 cc.Meanwhile, the inner core has a diameter of 0.75 inches and volume of3.62 cm. In one embodiment, the volume of the outer core layer isgreater than the volume of the inner core. In another embodiment, thevolume of the outer core layer and inner core are equivalent. In stillanother embodiment, the volume of the outer core layer is less than thevolume of the inner core. Other examples of core structures containinglayers of varying thicknesses and volumes are described below in TableA.

TABLE A Sample Core Dimensions Foamed Thermoset Inner Total Core TotalCore Outer Core Outer Core Core Volume of Example Diameter VolumeThickness Volume Diameter Inner Core A-C 0.30″  0.23 cc 0.100″  0.13 cc0.10″ 0.10 cc B-C 1.60″ 33.15 cc 0.750″ 33.05 cc 0.10″ 0.10 cc C-C 1.55″31.96 cc 0.225″ 11.42 cc 1.10″ 11.42 cc  D-C 1.55″ 31.96 cc 0.400″ 28.34cc 0.75″ 3.62 cc E-C 1.55″ 31.96 cc 0.525″ 28.34 cc 0.50″ 3.62 cc

Cover Structure

The golf ball sub-assemblies of this invention may be enclosed with oneor more cover layers. The golf ball sub-assembly may comprise themulti-layered core structure as discussed above. In other versions, thegolf ball sub-assembly includes the core structure and one or morecasing (mantle) layers disposed about the core. In one particularlypreferred version, the golf ball includes a multi-layered covercomprising inner and outer cover layers.

In one preferred embodiment, a thermoplastic ionomer composition is usedto form the inner cover. Such thermoplastic ionomers may be the samematerial used to form the outer core layer as described above. Preferredionomers are salts of O/X- and O/X/Y-type acid copolymers, wherein O isan α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid,and Y is a softening monomer. O is preferably selected from ethylene andpropylene. X is preferably selected from methacrylic acid, acrylic acid,ethacrylic acid, crotonic acid, and itaconic acid. Methacrylic acid andacrylic acid are particularly preferred. Y is preferably selected from(meth)acrylate and alkyl (meth)acrylates wherein the alkyl groups havefrom 1 to 8 carbon atoms, including, but not limited to, n-butyl(meth)acrylate, isobutyl (meth)acrylate, methyl (meth)acrylate, andethyl (meth)acrylate. These O/X- and O/X/Y-type acid copolymers, alongwith E/X and E/X/Y-type acid copolymers are described in detail above.

The inner cover layer is preferably formed from a composition comprisingan ionomer or a blend of two or more ionomers that helps impart hardnessto the ball. In a particular embodiment, the inner cover layer is formedfrom a composition comprising a high acid ionomer. A particularlysuitable high acid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is acopolymer of ethylene and methacrylic acid, having an acid content of 19wt %, which is 45% neutralized with sodium. In another particularembodiment, the inner cover layer is formed from a compositioncomprising a high acid ionomer and a maleic anhydride-graftednon-ionomeric polymer. A particularly suitable maleic anhydride-graftedpolymer is Fusabond 525D® (DuPont). Fusabond 525D® is a maleicanhydride-grafted, metallocene-catalyzed ethylene-butene copolymerhaving about 0.9 wt % maleic anhydride grafted onto the copolymer. Aparticularly preferred blend of high acid ionomer and maleicanhydride-grafted polymer is an 84 wt %/16 wt % blend of Surlyn 8150®and Fusabond 525D®. Blends of high acid ionomers with maleicanhydride-grafted polymers are further disclosed, for example, in U.S.Pat. Nos. 6,992,135 and 6,677,401, the entire disclosures of which arehereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

As noted above, the specific gravity (density) of the inner cover layeris an important property, because it affects the Moment of Inertia (MOI)of the ball. The composition used to form the inner cover layer of thisinvention is formulated to have relatively high specific gravity levels.The specific gravity of the inner cover is preferably greater than thespecific gravity of the outer core (SG_(inner cover)>SG_(outer core)).And, the specific gravity of the outer core is preferably greater thanthe specific gravity of the inner core (SG_(outer core)>SG_(center)) asdiscussed above. The inner cover layer has a relatively high specificgravity and this means more of the ball's overall mass is located awayfrom the ball's axis of rotation. Thus, the ball has a relatively highMoment of Inertia and tends to have a lower spin rate and longer flightdistance properties. In one preferred embodiment, the SG_(inner cover)is at least about 105%, preferably at least about 120% greater, than theSG_(outer core). For example, in one version, the SG_(inner cover) isabout 1.45 g/cc. and the SG_(outer core) is about 1.05 g/cc. Meanwhile,in one preferred embodiment, the SG_(outer core) is at least about 125%,preferably at least about 160% greater than the SG_(center). Forexample, in one version, the SG_(outer core) is about 1.05 g/cc and theSG_(center) is about 0.5 g/cc.

By the term, “specific gravity of the inner cover layer”(“SG_(inner cover)”), it is generally meant the specific gravity of theinner cover layer as measured at any point of the inner cover layer. Forexample, the inner cover layer may have a specific gravity within arange having a lower limit of about 1.00 or 1.10 or 1.25 or 1.30 or 1.36or 1.40 or 1.42 or 1.45 or 1.48 or 1.50 or 1.60 or 1.66 or 1.75 or 2.00g/cc and an upper limit of about 2.50 or 2.60 or 2.80 or 2.90 or 3.00 or3.10 or 3.25 or 3.50 or 3.60 or 3.80 or 4.00, 4.25 or 4.75 or 5.00 or5.10 g/cc.

The composition used to make the inner cover may include fillers toadjust the specific gravity of the composition as needed. Thesespecific-gravity adjusting fillers include high-density and low-densityfillers. Suitable fillers include, for example, metal (or metal alloy)powder, metal oxide, metal stearates, particulates, carbonaceousmaterials, and the like, and blends thereof. Examples of useful metal(or metal alloy) powders include, but are not limited to, bismuthpowder, boron powder, brass powder, bronze powder, cobalt powder, copperpowder, Inconel™ metal powder, iron metal powder, molybdenum powder,nickel powder, stainless steel powder, titanium metal powder, zirconiumoxide powder, aluminum flakes, tungsten metal powder, beryllium metalpowder, zinc metal powder, or tin metal powder. Examples of metal oxidesinclude, but are not limited to, zinc oxide, iron oxide, aluminum oxide,titanium dioxide, magnesium oxide, zirconium oxide, and tungstentrioxide. Examples of particulate carbonaceous materials include, butare not limited to, graphite and carbon black. Examples of other usefulfillers include but are not limited to graphite fibers, precipitatedhydrated silica, clay, talc, glass fibers, aramid fibers, mica, calciummetasilicate, barium sulfate, zinc sulfide, silicates, diatomaceousearth, calcium carbonate, magnesium carbonate, rubber regrind, manganesepowder, and magnesium powder, cotton flock, natural bitumen, celluloseflock, and leather fiber. Micro balloon fillers such as glass andceramic fillers also can be used.

Concerning the outer cover layer, which is disposed about the innercover, a wide variety of materials may be used to form this layer,including, for example, non-foamed thermoset or thermoplasticcompositions. More particularly, polyurethanes; polyureas; copolymers,blends and hybrids of polyurethane and polyurea; olefin-based copolymerionomer resins (for example, Surlyn® ionomer resins and DuPont HPF® 1000and HPF® 2000, commercially available from DuPont; Iotek® ionomers,commercially available from ExxonMobil Chemical Company; Amplify® IOionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The compositions used to make the inner and outer cover layers maycontain a wide variety of fillers and additives to impart specificproperties to the ball. For example, relatively heavy-weight andlight-weight fillers may be added to adjust the specific gravity of theinner and outer cover layers as discussed above. Other additivesinclude, but are not limited to, optical brighteners, coloring agents,fluorescent agents, whitening agents, UV absorbers, light stabilizers,surfactants, processing aids, antioxidants, stabilizers, softeningagents, fragrance components, plasticizers, impact modifiers, titaniumdioxide, clay, mica, talc, glass flakes, milled glass, and mixturesthereof.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 72 or 75 or 80 or 82 Shore C and an upperlimit of 85 or 86 or 88 or 90 or 92 Shore C. The thickness of the innercover layer is preferably within a range having a lower limit of 0.010or 0.015 or 0.020 or 0.030 inches and an upper limit of 0.035 or 0.045or 0.080 or 0.120 inches. The outer cover layer preferably has amaterial hardness of 85 Shore C or less. The thickness of the outercover layer is preferably within a range having a lower limit of 0.010or 0.015 or 0.025 inches and an upper limit of 0.035 or 0.040 or 0.055or 0.080 inches. Methods for measuring hardness of the layers in thegolf ball are described in further detail below. In one embodiment, theinner cover layer has an outer surface hardness(H_(outer surface of IC)) within a range having a lower limit of about45 or 47 or 50 or 52 or 54 or 58 or 60 or 62 or 65 Shore C and an upperlimit of about 68 or 70 or 72 or 75 or 78 or 80 or 81 or 85 or 86 or 90or 92 or 94 or 98 Shore C. Measuring according to a Shore D scale, inone embodiment, the inner cover layer has a (H_(outer surface of IC))within a range having a lower limit of about 40 or 44 or 48 or 51 or 52or 56 or 58 Shore D and an upper limit of about 60 or 64 or 68 or 70 or74 or 75 or 78 or 80 or 84 or 86 Shore D. Meanwhile, in one embodiment,the outer cover layer may have a surface hardness within a range havinga lower limit of about 20 or 26 or 30 or 34 or 38 or 42 or 44 or 48 or50 or 52 or 56 Shore D and an upper limit of about 60 or 64 or 66 or 67or 70 or 72 or 75 or 78 or 80 or 84 Shore D. In one embodiment, thesurface hardness of the outer core layer is greater than the centerhardness of the inner core and surface hardness of the inner coverlayer. In an alternative embodiment, the surface hardness of the outercore layer is less than the center hardness of the inner core andsurface hardness of the inner cover layer.

The core structure and inner cover also has a hardness gradient acrossthe core/inner cover assembly. As discussed above, in one embodiment,the (H_(inner core center)) is in the range of about 10 to about 60Shore C, preferably about 13 to about 55 Shore C and more preferablyabout 15 to about 50 Shore C; and the (H_(outer surface of OC)) is inthe range of about 65 to about 96 Shore C, preferably about 68 to about94 Shore C and more preferably about 75 to about 92 Shore C. Thus, apositive hardness gradient is provided across the core sub-assembly.

Meanwhile, in one such embodiment, the hardness of the outer surface ofthe inner cover (H_(outer surface of IC)) is in the range of about 60 toabout 98 Shore C, preferably about 64 to about 94 Shore C and morepreferably about 72 to about 88 Shore C. Thus, a positive hardnessgradient is provided across the core/inner cover assembly. The gradientacross the core/inner cover assembly will vary based on several factorsincluding, but not limited to, the dimensions of the inner core, outercore, and inner cover.

In FIG. 4, one version of a core/inner cover sub-assembly (30) for agolf ball is shown. The dual-layered core has a center (32) and outercore layer (34) surrounded by an inner cover (36). The geometric centerof the inner core (where the H_(inner core center) is measured);midpoint of the outer core layer (where the H_(midpoint of OC) ismeasured); and hardness of the outer surface of the inner cover (wherethe H_(outer surface of IC) is measured) are shown in FIG. 4.

Preferably, the inner cover is formed from a thermoplastic ionomericmaterial as discussed above, the outer cover layer is formed from apolyurethane material, and the outer cover layer has a hardness that isless than that of the inner cover layer. Preferably, the inner cover hasa hardness of greater than about 60 Shore D and the outer cover layerhas a hardness of less than about 60 Shore D. In an alternativeembodiment, the inner cover layer is comprised of a partially or fullyneutralized ionomer, a thermoplastic polyester elastomer such as Hytrel™commercially available form DuPont, a thermoplastic polyether blockamide, such as Pebax™ commercially available from Arkema, Inc., or athermoplastic or thermosetting polyurethane or polyurea, and the outercover layer is comprised of an ionomeric material. In this alternativeembodiment, the inner cover layer has a hardness of less than about 60Shore D and the outer cover layer has a hardness of greater than about55 Shore D and the inner cover layer hardness is less than the outercover layer hardness.

In yet another embodiment, a multi-layered cover comprising inner andouter cover layers is formed, where the inner cover layer has athickness of about 0.01 inches to about 0.06 inches, more preferablyabout 0.015 inches to about 0.040 inches, and most preferably about 0.02inches to about 0.035 inches. In this version, the inner cover layer isformed from a partially- or fully-neutralized ionomer having a Shore Dhardness of greater than about 55, more preferably greater than about60, and most preferably greater than about 65. The outer cover layer, inthis embodiment, preferably has a thickness of about 0.015 inches toabout 0.055 inches, more preferably about 0.02 inches to about 0.04inches, and most preferably about 0.025 inches to about 0.035 inches,with a hardness of about 80 Shore D or less, more preferably 70 or less,and most preferably about 60 or less. The inner cover layer is harderthan the outer cover layer in this version. A preferred outer coverlayer is a castable or reaction injection molded polyurethane, polyureaor copolymer, blend, or hybrid thereof having a Shore D hardness ofabout 40 to about 50. In another multi-layer cover, dual-coreembodiment, the outer cover and inner cover layer materials andthickness are the same but, the hardness range is reversed, that is, theouter cover layer is harder than the inner cover layer. For this harderouter cover/softer inner cover embodiment, the ionomer resins describedabove would preferably be used as outer cover material.

Manufacturing of Golf Balls

As described above, the inner core preferably is formed by a castingmethod. The outer core layer, which surrounds the inner core, is formedby molding compositions over the inner core. Compression or injectionmolding techniques may be used to form the other layers of the coresub-assembly. Then, the casing and/or cover layers are applied over thecore sub-assembly. Prior to this step, the core structure may besurface-treated to increase the adhesion between its outer surface andthe next layer that will be applied over the core. Suchsurface-treatment may include mechanically or chemically-abrading theouter surface of the core. For example, the core may be subjected tocorona-discharge, plasma-treatment, silane-dipping, or other treatmentmethods known to those in the art.

The cover layers are formed over the core or ball sub-assembly (the corestructure and any casing layers disposed about the core) using asuitable technique such as, for example, compression-molding,flip-molding, injection-molding, retractable pin injection-molding,reaction injection-molding (RIM), liquid injection-molding, casting,spraying, powder-coating, vacuum-forming, flow-coating, dipping,spin-coating, and the like. Preferably, each cover layer is separatelyformed over the ball subassembly. For example, an ethylene acidcopolymer ionomer composition used to form the inner cover, as describedabove, may be injection-molded to produce half-shells. Alternatively,the ionomer composition may be placed into a compression mold and moldedunder sufficient pressure, temperature, and time to produce thehemispherical shells. The smooth-surfaced hemispherical shells are thenplaced around the core sub-assembly in a compression mold. Undersufficient heating and pressure, the shells fuse together to form aninner cover layer that surrounds the sub-assembly. In another method,the ionomer composition is injection-molded directly onto the coresub-assembly using retractable pin injection molding. An outer coverlayer comprising a polyurethane or polyurea composition over the ballsub-assembly may be formed by using a mold-casting process.

In one such casting process. a polyurethane prepolymer and curing agentare mixed in a motorized mixer inside of a mixing head by meteringamounts of the curative and prepolymer through the feed lines. A moldhaving upper and lower hemispherical-shaped mold cavities and withinterior dimple patterns is used. (72 a) and (74 a). Each mold cavityhas an arcuate inner surface defining an inverted dimple pattern. Theupper and lower mold cavities can be preheated and filled with thereactive polyurethane and curing agent mixture. After the reactivemixture has resided in the lower mold cavities for a sufficient timeperiod, typically about 40 to about 100 seconds, the golf ballcore/inner cover assembly can be lowered at a controlled speed into thereacting mixture. Ball cups can hold the assemblies by applying reducedpressure (or partial vacuum). After sufficient gelling (typically about4 to about 12 seconds), the vacuum can be removed and the assembly canbe released. Then, the upper half-molds can be mated with the lowerhalf-molds. An exothermic reaction occurs when the polyurethaneprepolymer and curing agent are mixed and this continues until thematerial solidifies around the subassembly. The molded balls can then becooled in the mold and removed when the molded cover layer is hardenough to be handled without deforming. This molding technique isdescribed in the patent literature including Hebert et al., U.S. Pat.No. 6,132,324, Wu, U.S. Pat. No. 5,334,673, and Brown et al., U.S. Pat.No. 5,006,297, the disclosures of which are hereby incorporated byreference.

As discussed above, the lower and upper mold cavities have interiordimple cavity details. When the mold cavities are mated together, theydefine an interior spherical cavity that forms the cover for the ball.The cover material encapsulates the inner ball subassembly to form aunitary, one-piece cover structure. Furthermore, the cover materialconforms to the interior geometry of the mold cavities to form a dimplepattern on the surface of the ball. The mold cavities may have anysuitable dimple arrangement such as, for example, icosahedral,octahedral, cube-octahedral, dipyramid, and the like. In addition, thedimples may be circular, oval, triangular, square, pentagonal,hexagonal, heptagonal, octagonal, and the like.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball. In FIG. 5, a finished golf (38)having a dimpled outer cover made in accordance with the presentinvention is shown. As discussed above, various patterns and geometricshapes of the dimples (40) can be used to modify the aerodynamicproperties of the golf ball.

Different ball constructions can be made using the core and coverconstructions of this invention as shown in FIGS. 1-5. Such golf ballconstructions include, for example, five-piece, and six-piececonstructions. It should be understood that the golf ball components andgolf balls shown in FIGS. 1-5 are for illustrative purposes only, andthey are not meant to be restrictive. Other golf ball constructions canbe made in accordance with this invention.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used. Likewise,the midpoint of a core layer is taken at a point equidistant from theinner surface and outer surface of the layer to be measured, mosttypically an outer core layer. Once again, once one or more core layerssurround a layer of interest, the exact midpoint may be difficult todetermine, therefore, for the purposes of the present invention, themeasurement of “midpoint” hardness of a layer is taken within plus orminus 1 mm of the measured midpoint of the layer.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore A, Shore Cor Shore D hardness) was measured according to the test method ASTMD-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Drop Rebound.

By “drop rebound,” it is meant the number of inches a sphere willrebound when dropped from a height of 72 inches in this case, measuringfrom the bottom of the sphere. A scale, in inches is mounted directlybehind the path of the dropped sphere and the sphere is dropped onto aheavy, hard base such as a slab of marble or granite (typically about 1ft wide by 1 ft high by 1 ft deep). The test is carried out at about72-75° F. and about 50% RH

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball sub-assembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

Density.

The density refers to the weight per unit volume (typically, g/cm³) ofthe material and can be measured per ASTM D-1622.

EXAMPLES

The present invention is illustrated further by the following Examples,but these Examples should not be construed as limiting the scope of theinvention.

In the following Examples, different foam formulations were used toprepare core samples using the above-described molding methods. Thedifferent formulations are described in Tables 1-3 below. Theconcentrations are in parts per hundred (phr), unless otherwiseindicated. As used herein, the term “parts per hundred,” also known as“phr,” is defined as the number of parts by weight of a particularcomponent present in a mixture, relative to 100 parts by weight of thebase component. Mathematically, this can be expressed as the weight ofan ingredient divided by the total weight of the polymer, multiplied bya factor of 100.

TABLE 1 Spherical Foam Core Samples Example No. 1 2 3 4 5 6 6.5% MDIPrepolymer 41.00 43.72 45.01 33.58 49.48 31.83 Mondur MR 7.33 13.64Mondur CD 19.75 Mondur ML 17.00 13.06 8.06 Poly THF 650 22.20 13.0629.01 CAPA 3031 13.77 13.77 4.00 CAPA 3091 27.86 CAPA 4101 CAPA 4801D.I. Water 0.50 0.50 0.45 0.50 0.45 0.50 Niax 1500 0.75 0.75 0.75 0.750.75 Varox MPBC Irganox 1135 Dabco 33LV 0.20 0.20 0.20 0.20 0.20Garamite 1958 0.38 0.38 0.38 0.38 0.38 Total Parts 76.35 76.32 76.3276.33 75.05 76.31 Density 0.54 0.70 0.60 0.53 0.60 Compression 35 106−217 −242 −217 COR @125 ft/s 0.434 0.503 0.520 0.278 0.4106.5% MDI Prepolymer is made from 4,4′-MDI and polytetramethylene glycolether (PTMEG 2000) (2000 m. w.).Mondur™ MR—polymeric MDI, available from Bayer.Mondur™ CD—modified 4,4′-MDI, available from Bayer.Mondur™ ML—isomer mixture of 2,4 and 4,4′-MDI, available from Bayer.Poly THF™ 650-650 molecular weight polyetratmethylene ether glycol(PTMEG), available from BASF.CAPA™ 3031—low molecular weight trifunctional polycaprolactone polyol,available from Perstorp.CAPA™ 3091—polyester triol terminated by primary hydroxyl groups,available from Perstorp.CAPA™ 4101—tetra-functional polyol terminated with primary hydroxylgroups, available from Perstorp.CAPA™ 4801—tetra-functional polyol terminated with primary hydroxylgroups, available from Perstorp.Niax™ L-1500—silicone surfactant available from Momentive SpecialtyChemicals, Inc.Vanox™ MBPC—antioxidant, available from R.T. Vanderbuilt.Irganox™ 1135—antioxidant, available from BASF.Dabco™ 33LV—tertiary amine catalyst, available from Air Products.Garamite™ 1958—mixed mineral thixotropes (clay mixture), available fromSouthern Clay Products.

TABLE 2 Spherical Foam Core Samples Example No. 7 8 9 10 11 12 6.5% MDI21.67 45.81 49.22 45.01 45.01 55.80 Prepolymer Mondur MR 18.46 7.46 8.017.33 7.33 9.08 Mondur CD Mondur ML Poly THF 650 34.33 20.57 13.00 22.2022.20 CAPA 3031 0.70 4.00 9.66 CAPA 3091 CAPA 4101 CAPA 4801 D.I. Water0.53 0.45 0.45 0.45 0.45 0.45 Niax 1500 0.75 0.75 0.75 0.75 0.75 0.75Varox MPBC 0.38 Irganox 1135 0.38 Dabco 33LV 0.20 0.20 0.20 0.20 0.200.20 Garamite 1958 0.38 0.38 0.38 0.38 0.38 0.38 Total Parts 76.32 76.3276.01 76.69 76.70 76.32 Density 0.46 0.4 Compression −245 −109 COR @125ft/s 0.388 0.515

TABLE 3 Spherical Foam Core Samples Example No. 13 14 15 16 17 18 6.5%MDI Prepolymer 68.81 44.28 33.10 42.39 49.48 40.75 Mondur MR 12.49 17.0511.96 8.06 11.50 Mondur CD Mondur ML Poly THF 650 CAPA 3031 5.79 5.052.86 2.37 2.00 CAPA 3091 CAPA 4101 12.67 21.48 17.79 15.00 22.27 CAPA4801 D.I. Water 0.39 0.45 0.67 0.48 0.45 0.48 Niax 1500 0.75 0.75 0.750.75 0.75 0.75 Varox MPBC Irganox 1135 Dabco 33LV 0.20 0.20 0.20 0.200.20 0.20 Garamite 1958 0.38 0.38 0.38 0.38 0.38 0.38 Total Parts 76.3276.26 76.49 76.32 76.32 76.33 Density 0.52 0.35 0.64 0.39 0.46 0.39Compression −200 −144 45 −135 −165 −120 COR @125 ft/s 0.540 0.534 0.5710.553 0.537 0.543

TABLE 4 Spherical Foam Core Samples Example No. 19 20 21 22 23 24 6.5%MDI Prepolymer 47.83 56.05 29.18 19.58 43.87 50.63 Mondur MR 7.78 9.1212.51 16.68 9.63 5.63 Mondur CD Mondur ML Poly THF 650 2.65 2.31 CAPA3031 CAPA 3091 CAPA 4101 18.92 18.11 17.37 20.23 18.36 15.98 CAPA 480116.10 15.44 17.98 D.I. Water 0.45 0.61 0.50 0.52 0.47 0.45 Niax 15000.75 0.75 0.75 0.75 0.75 0.75 Varox MPBC Irganox 1135 Dabco 33LV 0.200.20 0.20 0.20 0.20 0.20 Garamite 1958 0.38 0.38 0.38 0.38 0.38 0.38Total Parts 76.31 101.32 76.33 76.32 76.31 76.33 Density 0.42 0.66 0.510.46 0.57 Compression −165 −169 −100 −164 −169 COR @125 ft/s 0.609 0.4920.425 0.578 0.566

TABLE 5 Spherical Foam Core Samples Example No. 25 26 6.5% MDIPrepolymer 37.21 43.57 Mondur MR 13.07 9.56 Mondur CD Mondur ML Poly THF650 3.06 5.25 CAPA 3031 CAPA 3091 CAPA 4101 21.18 16.15 CAPA 4801 D.I.Water 0.49 0.47 Niax 1500 0.75 0.75 Varox MPBC Irganox 1135 Dabco 33LV0.20 0.20 Garamite 1958 0.38 0.38 Total Parts 76.34 76.33 Density 0.430.45 Compression −137 −147 COR @125 ft/s 0.541 0.571

Different foam formulations were used to prepare foam centers in thefollowing examples. A thermoset rubber formulation was molded about thefoam centers to form an outer core layer. The above-described moldingmethods were used to prepare the samples. The resulting dual-coreassemblies (Samples A-C) were tested for compression (DCM), Coefficientof Restitution (COR), and Hardness using the above-described testmethods and the results are reported in Table 10 below.

Sample A (Dual Core Having 0.5″ Foamed Center)

In Sample A, the following foam formulation (Table 6) was used toprepare an inner core having a diameter of 0.5 inches. The followingrubber formulation (Table 7) was molded about the foamed inner core andcured to form an outer-core.

TABLE 6 (Foam Center of Sample A - 36) Ingredient Parts 6.5% MDIPrepolymer 45.01 Mondur ™ MR 7.33 Poly THF ™ 650 22.20 Deionized Water0.45 Niax ™ L-1500 surfactant 0.75 Dabco ™ 33LV 0.20 Garamite ™ 19580.38

TABLE 7 (Rubber Outer Core Layer of Sample A) Ingredient Parts *Buna ™CB23 100.0 Zinc Diacrylate (ZDA) 35.0 **Perkadox BC 0.5 ZincPentachlorothiophenol (ZnPCTP) 0.7 Zinc Oxide 5.0 *Buna ™ CB23 -polybutadiene rubber, available from Lanxess Corp. **Perkadox ™ BC,peroxide free-radical initiator, available from Akzo Nobel.

Sample B (Dual Core Having 0.5″ Foamed Center—48)

In Sample B, the following foam formulation (Table 8) was used toprepare an inner core having a diameter of 0.5 inches. The same rubberformulation used in Sample A (Table 7) was molded about the foamed innercore and cured to form an outer core layer.

TABLE 8 (Foam Center of Sample B) Ingredient Parts 6.5% MDI Prepolymer55.80 Mondur ™ MR 9.08 CAPA ™ 3031 9.66 Deionized Water 0.45 Niax ™L-1500 surfactant 0.75 Dabco ™ 33LV 0.20 Garamite ™ 1958 0.38

In Sample C, the following foam formulation (Table 9) was used toprepare an inner core having a diameter of 0.5 inches. The same rubberformulation used in Sample A (Table 7) was molded about the foamed innercore and cured to form an outer core layer.

TABLE 9 (Foam Center of Sample C - 50) Ingredient Parts 6.5% MDIPrepolymer 44.28 Mondur ™ MR 12.49 CAPA ™ 3031 5.05 CAPA ™ 4101 12.67Deionized Water 0.45 Niax ™ L-1500 surfactant 0.75 Dabco ™ 33LV 0.20Garamite ™ 1958 0.38

TABLE 10 Properties of Dual-Core Samples Diameter Size Surface CenterHardness and Density of Compression COR @ Hardness Hardness GradientSample Foam Center (DCM) 125 ft/sec (Shore C) (Shore C) (Shore C) A 0.5inches and 85 0.816 88.9 22.1 66.8 0.5 g/cc. B 0.5 inches and 81 0.79786.1 46.0 40.1 0.5 g/cc. C 0.5 inches and 81 0.806 87.0 43.7 43.3 0.5g/cc.

As shown in Table 10 above, the dual-layered core samples A, B, and Cwere tested for hardness and the core was found to have a hardnessgradient (across the entire core as measured at points in millimeters(mm) from the geometric center to the outer surface of the outer corelayer) in the range of about 20 Shore C to about 90 Shore C. In SampleA, the hardness of the foam core measured at the geometric center wasabout 22 Shore C and the hardness of the core measured at about 20 mmfrom the geometric center (that is, the surface of the outer core layer)was about 90 Shore C. In Sample B, the hardness gradient from the foamcenter to the surface of the rubber outer core layer was about 40 ShoreC; and in Sample C, the hardness gradient from the foam center to thesurface of the rubber outer core layer was about 43 Shore C. Themidpoint hardness of the outer core layer (H_(midpoint of OC)) in eachof Samples A, B, and C was about 75 Shore C.

In Sample D, the following foam formulation (Table 11) was used toprepare an inner core having a diameter of 0.75 inches. The same rubberformulation used in Sample A (Table 7) was molded about the foamed innercore and cured to form an outer core layer. The above-described moldingmethods were used to prepare the samples. Different dual-core assemblieshaving different densities (Samples D1-D5) were prepared and tested forcompression (DCM), Coefficient of Restitution (COR), and Hardness usingthe above-described test methods and the results are reported in Table12 below.

TABLE 11 (Foam Center of Sample D - 55) Ingredient Parts 6.5% MDIPrepolymer 47.83 Mondur ™ MR 7.78 CAPA ™ 4101 18.92 Deionized Water 0.45Niax ™ L-1500 surfactant 0.75 Dabco ™ 33LV 0.20 Garamite ™ 1958 0.38

TABLE 12 Properties of Core Samples (D1-D5) Density Diameter of Size ofFoamed Surface Center Hardness Foamed Center Compression COR @ HardnessHardness Gradient Sample Center (g/cm³) (DCM) 125 ft/sec (Shore C)(Shore C) (Shore C) D-1 0.75″ 0.40 80 0.779 86.6 33.5 53.0 D-2 0.75″0.46 78 0.775 86.4 32.1 54.3 D-3 0.75″ 0.59 77 0.770 86.4 34.1 52.3 D-40.75″ 0.75 78 0.769 87.3 43.0 44.3 D-5 0.75″ 0.83 75 0.766 87.4 37.450.0

As shown in Table 12 above, the dual-layered core Samples D-1 to D-5were tested for hardness and the core was found to have a hardnessgradient (across the entire core as measured at points in millimeters(mm) from the geometric center to the outer surface of the outer corelayer) in the range of about 44 Shore C to about 55 Shore C. Forinstance, in Sample D-1, the hardness of the core measured at thegeometric center was about 34 Shore C and the hardness of the coremeasured at about 20 mm from the geometric center (that is, the surfaceof the outer core layer) was about 87 Shore C.

In the following Examples, different foam formulations (Samples E-G)were used to prepare foam centers (Table 13). A rubber formulation(Table 14) was molded about each of the foam centers and cured to forman outer core layer. The resulting dual-core sub-assemblies (foamcenter/thermoset rubber outer core layer) were encapsulated with aninner cover layer comprising an ethylene acid copolymer ionomercomposition (Table 15). The above-described molding methods were used toprepare the samples. Different dual-core/inner-cover assemblies havingdifferent foam center diameters (Samples E1, E2, F1, F2, G1, and G2)were prepared and tested for compression (DCM), Coefficient ofRestitution (COR), and Hardness using the above-described test methodsand the results are reported in Table 16 below.

TABLE 13 (Foam Center of Samples E-G) Sample E (51) Sample F (55) SampleG (60) Ingredients (Parts) (Parts) (Parts) 6.5% MDI 33.10 47.83 50.63Prepolymer Mondur ™ MR 17.05 7.78 5.63 Poly THF ™ 650 2.31 CAPA ™ 30312.86 CAPA ™ 4101 21.48 18.92 15.98 Deionized Water 0.67 0.45 0.45 Niax ™L-1500 0.75 0.75 0.75 surfactant Dabco ™ 33LV 0.20 0.20 0.20 Garamite ™1958 0.38 0.38 0.38

TABLE 14 (Rubber Outer Core Layer of Samples E-G) Ingredient PartsBuna ™ CB23 100.0 Zinc Diacrylate (ZDA) 36.0 Perkadox BC 0.5 ZincPentachlorothiophenol (ZnPCTP) 0.5 Zinc Oxide 21.3

TABLE 15 (Tungsten-Filled Inner Cover Layer of Samples E-G) IngredientConcentration Blend of 50% Surlyn ™ 7940 and 50% 72.5 wt. % (98.1 vol.%) Surlyn ™ 8940 ethylene acid copolymer ionomer resins. Tungsten Filler27.5 wt. % (1.9 vol. %)

TABLE 16 Properties of Dual-Core/Inner Cover Samples (E1-G2) OuterSurface Center Density Density Hardness Hardness Diameter of of of Innerof Foam Hardness Size of Foamed Inner Cover Center Gradient FoamedCenter Compression COR @ Cover (Shore (Shore (Shore Sample Center(g/cm³) (DCM) 125 ft/sec (g/cm³) C) C) C) E-1 0.50″ 0.50 92 0.813 1.3093.0 52.0 41.00 E-2 0.75″ 0.50 97 0.781 1.45 92.2 48.0 44.20 F-1 0.50″0.50 88 0.814 1.30 91.7 29.0 62.70 F-2 0.75″ 0.50 101 0.798 1.45 94.427.0 67.40 G-1 0.50″ 0.50 87 0.816 1.30 92.4 19.0 73.40 G-2 0.75″ 0.5099 0.808 1.45 92.9 18.0 74.90

As shown in Table 16, the dual-layered core/inner cover assembly SamplesE-1 and E-2 were tested for hardness and the assemblies were found tohave a hardness gradient (across the entire structure as measured atpoints in millimeters (mm) from the geometric center to the outersurface of the inner cover layer) of about 41.00 and 44.2 Shore C,respectively. Samples F-1 and F-2 also were tested and the hardnessgradients were about 62.70 and 67.40 Shore C, respectively. Finally,Samples G-1 and G-2 were tested, and the hardness gradients were about73.40 and 74.90 Shore C, respectively.

The hardness properties of Samples E1-G2, as measured per a Shore Ascale, are described below in Table 17.

TABLE 17 Shore A Hardness of Dual-Core/Inner Cover Samples E1-G2 CenterDensity Density Hardness Diameter of of of Foam Size of Foamed Compres-COR @ Inner Center Foamed Center sion 125 ft/ Cover (Shore Sample Center(g/cm³) (DCM) sec (g/cm³) A) E-1 0.50″ 0.50 92 0.813 1.45 89 E-2 0.75″0.50 97 0.781 1.45 86 F-1 0.50″ 0.50 88 0.814 1.45 67 F-2 0.75″ 0.50 1010.798 1.45 63 G-1 0.50″ 0.50 87 0.816 1.45 42 G-2 0.75″ 0.50 99 0.8081.45 39

In the following Examples, the dual-core (foam center/thermoset rubberouter core layer) inner cover (ethylene acid copolymer ionomercomposition) assemblies as described above (Samples E1-G2) wereencapsulated with an outer cover. Particularly, a polyurethanecomposition was cast-molded over the dual-core/inner cover assemblies toform finished balls. These balls are identified as Samples (E1-G2) inbelow Table 18, and the Moment of Inertia (MOI) for these ball samplesis included in the Table.

TABLE 18 MOI of Finished Ball Samples E1-G2 Diameter Size of FoamedSample (Finished Ball) Center MOI (g/cm²) E-1 0.50″ 83.84 E-2 0.75″85.75 F-1 0.50″ 85.53 F-2 0.75″ 85.51 G-1 0.50″ 83.63 G-2 0.75″ 86.37

It is understood that the golf ball compositions, constructions, andproducts described and illustrated herein represent only someembodiments of the invention. It is appreciated by those skilled in theart that various changes and additions can be made to compositions,constructions, and products without departing from the spirit and scopeof this invention. It is intended that all such embodiments be coveredby the appended claims.

We claim:
 1. A multi-layered golf ball, comprising: a core assemblycomprising: i) an inner core layer comprising a foamed composition, theinner core layer having a diameter in the range of about 0.100 to about1.100 inches and a specific gravity (SG_(inner)) and a center hardness(H_(inner core center)); and ii) an outer core layer comprising anon-foamed thermoset or thermoplastic composition, the outer core layerbeing disposed about the inner core layer and having a thickness in therange of about 0.100 to about 0.750 inches and a specific gravity(SG_(outer)) and an outer surface hardness (H_(outer surface of OC));and a multi-layered cover comprising: i) an inner cover layer comprisinga non-foamed thermoplastic ionomer composition having a specific gravity(SG_(inner cover)), the ionomer composition comprising an O/X-type acidcopolymer, wherein O is α-olefin, and X is a C₃-C₈α,β-ethylenicallyunsaturated carboxylic acid; and ii) an outer cover layer comprising anon-foamed thermoset or thermoplastic composition, wherein theSG_(inner cover)>SG_(outer core)>SG_(center) and theH_(inner core center) is in the range of about 10 to about 60 Shore Cand the H_(outer surface of OC) is in the range of about 65 to about 96Shore C to provide a positive hardness gradient across the coreassembly.
 2. The golf ball of claim 1, wherein the O of the O/X-typeacid copolymer is selected from the group consisting of ethylene andpropylene, and X is selected from the group consisting of methacrylicacid, acrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaricacid, and itaconic acid.
 3. The golf ball of claim 2, wherein the O ofthe O/X-type acid copolymer is ethylene and the X is methacrylic acid oracrylic acid.
 4. The golf ball of claim 1, wherein the O/X-type acidcopolymer contains acid groups and 30 to 70% of the acid groups areneutralized.
 5. The golf ball of claim 1, wherein the O/X-type acidcopolymer contains acid groups and greater than 70% of the acid groupsare neutralized.
 6. The golf ball of claim 1, wherein the ionomercomposition further comprises fatty acids or salts of fatty acids. 7.The golf ball of claim 1, wherein the ionomer composition comprises ablend of O/X-type acid copolymers, wherein O is α-olefin, and X is aC₃-C₈ α,β-ethylenically unsaturated carboxylic acid.
 8. The golf ball ofclaim 1, wherein the foamed composition is a foamed polyurethanecomposition.
 9. The golf ball of claim 1, wherein the outer core layercomprises a thermoset rubber selected from the group consisting ofpolybutadiene, ethylene-propylene rubber, ethylene-propylene-dienerubber, polyisoprene, styrene-butadiene rubber, polyalkenamers, butylrubber, halobutyl rubber, polystyrene elastomers, copolymers ofisobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and mixtures thereof.
 10. Thegolf ball of claim 1, wherein the outer core layer comprises athermoplastic polymer selected from the group consisting ofpartially-neutralized ionomers; highly-neutralized ionomers; polyesters;polyamides; polyamide-ethers, polyamide-esters; polyurethanes,polyureas; fluoropolymers; polystyrenes; polypropylenes; polyethylenes;polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinylalcohols; polyester-ethers; polyethers; polyimides, polyetherketones,polyamideimides; and mixtures thereof.